I understand the desire to keep it non-descript, but I'm glad you clarified.
I know that for me, my husband and I have 20-year relationship under our belts. The power dynamic between us is practically fixed in stone, and change is slow, at best. He would love for me to become submissive (heck, he'd love for me to become dominant too, just for fantasy giggles). I am slowly dipping my toe into the submissive waters with him, because he's tried some new things that I respond too naturally. Unfortunately, I have not been able to "just give him what he wants" entirely. You would think it would be that simple, and yet, the pressure from him (even unspoken) is strong, and I do not respond well to sexual pressure. If I try, I become resentful, and that's no good for us. It may be a straight up personality flaw, but so it is.
With my secondary, we met through swinging, so there was an immediate sexual connection that developed into an emotional connection over time. The sexual and power dynamics were vastly different from those with my primary from the start. With the secondary, I have a strong urge to submit. I can only guess that there is something about the secondary's non-verbal communication style (between touch and eye contact) that triggers it. I can honestly say it is not love that triggers it, for the desire to submit was there almost immediately, even when submission was not sought.
I can offer no advice about how to feel better about the difference. I know my husband links his sexual relationship with me to his feelings of self-worth, so there is no easy way to deal with it. I can only suggest you move in the direction you want to move with your primary. Try some new things, but try to avoid making it a competition with the secondary (even in your own head).
Some things to consider... do you really need to know what they do sexually? If so, be honest about what will bother you. In my case, it's easier to simply not pursue things than to hurt my husband's feelings.