I haven't read the entire thread. My wife and I just celebrated 10 years. My wife is frugal. I'd spend every cent if I could :-) One of the best things we EVER did was work out discretionary funds up front. Money we each get for the month that is ours to spend however we want. If I don't spend mine it goes into MY savings account. She would not be pleased if out of the blue I said I wanted to drop 2k on a new DAC. Who would? On the other hand, If I saved the money and bought the DAC.... I do occasionally take out a loan to buy something used off of Audiogon or here, but I present a clear path for paying it off. I typically have to sell something in order to pay off the "debt". Objectively, we could all "collect" a bunch of stuff in our "hobby". This helps thin the heard as well. Additionally, as many have mentioned, get her into the music. I got out of headphones and into speakers to make this part work. It does work, and she enjoys the music as much as I do.
My wife and I have a similar arrangement. I have a set amount from each paycheck go into a personal savings account, which i can spend as I wish. From time to time, I make some purchases from household funds, but my hobby stuff (audio and photography - both major cash sinks) come out of my savings.