Ok, I get the distinction you're making with the playing-with-others-together-but-never-separately =/= non-exclusivity thing. It's not the way I would wanna do non-monogamy, but I'm certainly not going to tell you it's not the way to go when it's made you happy for ten years.
I'm sorry you've felt so attacked in this thread. I won't try to tell you any further that you shouldn't look for what you're looking for, and will instead think about where all this is coming from on our ends, and share some general thoughts that may be of use to you as you move forward.
I've been thinking about this thread in comparison to this thread -- http://www.polyamory.com/forum/showthread.php?t=16979
-- and asking myself why, exactly, do we think "unexpected polyfi triad = sounds great" and "planning on a polyfi triad = sounds like trouble"? Relatedly, why does this graphic exist -- http://www.obsidianfields.com/lj/polyprivilege.gif
Veau talks in the graphic about privilege and entitlement... getting special treatment and feeling like you're owed special treatment. If one takes his analysis to be correct, then one way to interpret it is that unicorn-hunting is problematic because it makes the statement "what we've built is special and someone new should join us, rather than us trying to reshape what we've built to fit someone new."
I have mixed feelings about the graphic. I find it funny, but I also find it to be a bit harsh to unicorn-hunters, as many in this community are. Surely, the vast majority of hunters, like you guys, have only the best intentions. So, again, why does the sort of search you're engaged in have such a bad rap? Why is it awesome if it happens accidentally but not-so-hot when it's sought?
All I have to go on here are my own experiences and the stories of others that I've read. And I think a lot of it is the stories. I feel like I'm getting repetitive when I talk about horror stories, but it really is true... we see too many sad folks who tried what you're trying from one end or the other and had it explode. Whereas when people find a triad serendipitously it doesn't seem to explode in quite the same way (all this talk of explosions... I feel like we're all mad scientists engaging in love experiments now
So... well, I *know* I'm being repetitive now, but... why?? Why don't we have more (any? not sure, but I haven't seen one yet) happy stories of successful unicorn hunts when we have a whole thread just for success stories in the blog section?
If I had to guess, I'd say it's because human relationships are crazy-complex. Between two people it's tough enough, but with three it becomes exponential. Almost always, things work differently than you think they will in one particular or another. With a vee, you really just have two two person relationships, so it's not *quite* as unpredictable. But a three-person marriage, no matter who's having sex with whom, is a triad. Staying flexible seems like the best way to ensure success. Note that in the thread above the existing couple has already been through a couple of permutations, from a vee to a triad and from casual to serious. If they'd started out thinking that the way they'd begun was the way it had to stay, there'd be one or more broken hearts between the three of them by now.
When you start out saying I want this sort of naturally complex, unpredictable relationship and it needs to be *precisely* this way, people wince. Because you *might* get lucky, but you're more likely heading for an explosion. Knowing what you want isn't enough, because everyone can start on the same page and then discover that things have shifted. If only one structure is acceptable to you, and the threeway-love you find doesn't end up fitting that structure, what can you do but end it? But by the time real bonds of love have been established, it's often not so easy to just pull the plug.
That's why I was so appreciative of the fact that you guys recognized that your new person might become a lover, emotionally and/or sexually, to one of you but not necessarily to both. I think that is a type of flexibility that is absolutely crucial to actively seeking a new partner as a couple. Technically one could say that, polygamous marriage goal or not, the fact that you two don't require your third to love you both the same means you're not "true" unicorn hunters, and it may well be that you're getting flack because of the poor performance of people who are after something very similar but more rigid than what you're after. Clearly there are some things you're not willing to bend on, but I would encourage you to hang on to that flexibility to the extent that you can -- my guess is that it will serve you well.
The other major point of concern, aside from the need for flexibility in complex scenarios, are the imbalances inherent whenever a new person joins a long-established couple (for this I can draw more on my own experience, in addition to stories). That imbalance is the reason I pretty much always share that couple-dating article I posted previously with anyone in a situation remotely similar to yours.
As I described above, a large source of potential imbalance comes from the tendency of an unattached person who wants to join a couple to be younger and/or less experienced. I won't rehash that point, but you can see how someone in that position could end up accepting things that make them feel used without knowing that they're not respecting their own boundaries. So, I would encourage you to be wary of anyone who's more than a couple of years younger than you, who hasn't dated much, or who just gives off an aura of being a bit naive.
Setting the question of age/experience aside, it's just easy, generally, to find yourself a little cowed by a relationship that's existed for a long time when you're trying to become a part of it. Two people who have been building a partnership together for many years have their own rituals, their own private language, that forms a sort of wall that can take years for an outsider to scale, even when the couple is trying to let the person in. There's just so much history there, so many compromises that they've devised to fit them perfectly. How does the new person find a place of comfort for their own unique ways of doing things without feeling like there's either no space for them or like they're breaking apart the things the couple has already built?
These are huge challenges for the new person which the couple may naturally be blind to, the way a fish isn't actively aware of water. It takes a very sensitive awareness of what the new person is going through and a willingness to bend and accept changes to the existing relationship beyond what you may have initially anticipated to truly build a place where the new person is an insider. I would encourage you to make peace with the idea that if you find what you want, your lives together will never be quite the same. Like having a kid, but moreso even. You will be building something new, just like you built a new life when the two of you first embarked on the journey of marriage. I think a lot of unicorn-hunting horror stories come about because couples didn't realize this fact and freaked out when they saw their relationship changing to accommodate a whole new human being. I see you've acknowledged above that you will need to work on the marriage and that it will be complex, and I think that's an excellent place to be starting from.
Phew! Long post is long.
I hope you'll keep posting and let us know how it goes, the good and the bad. Again, I know you feel like you've gotten a poor reception here, but none of us are so petty that we'd waste all these words if we weren't genuinely trying to help. For myself at least, I can promise that I'll keep an open mind, try to help you with the hard stuff and celebrate your successes with you. You can always post in big letters at the top of a potential blog "we will not discuss the feasibility of the premise of unicorn hunting" if you're worried that any attempt to talk about how things are going wil just get derailed by this hot topic.