Here's my thought based on my life.. Some of this will pertain to you and I'm sure that some will not. My husband and I have been married 2 years and together 3. He was very up front when we started dating that he was interested in a poly lifestyle. At first he wanted to experience 3 somes and occasional random hookups. Not exactly the poly lifestyle (while the random hookups). I am not into women as much and wasn't really feeling the whole 3some thing especially in a new relationship (I still feel that way). As far as a poly I had told him that in order for anything like that to work we needed a strong relationship first. The subject has been dropped for 3 years and just recently been resurrected. I still belive that in order for a poly to work your primary should be strong. I don't think that you should go into a poly relationship because your marriage now isn't working. This is just going to lead to confusion and resentment.
I know I am new to this and technically I have never been in a poly relationship. Though being how my husband was upfront front the beginning, I have had 3 years to learn about this, myself, our marriage, and relationships in general. Our idea for a poly is that we would have someone else to fulfill aspects that maybe he or I can not. His idea of what he wants has also changed in 3 years. We now have a family and we know eachother much better and are still learning. He no longer craves those random hookups or the idea of a 3some. He respects me much more and respects what I need and want. In turn I do too. I have known that this would eventually be an issue in our relationship if I was to just turn my back to what he wanted. Any relationship takes work and compromise. I have been given the time to think about it. Though I was never closed off to the idea comepletely.
Now that we are speaking about it again, we are trying to figure our boundaries, complications, and what we want. He has even said that another couple would probably be the best of us. I agree. Right now we are trying to wade through all of this, the what ifs, and the rules before we even think about finding another couple. If your wife is already tuning you out and communication is broken down I don't think she would be very open to an alternative lifestyle as this.
As I have learned recently sometimes the best thing in life is clarity smacking you in the face. Maybe you just need to be upfront with her and tell her where you see your marriage sitting at. That might be a better route then telling her you want a relationship with someone else. I hope this helps