I'd love to get into quad, never could afford it back in the day. Nobody I knew had it so I have no idea what it is like. I've been curious for forty years. It may never be though, I've started getting the "you've got more stuff than you can use now".
Good luck on the hunt and let me know how you like quad.
Here's my story: I got a killer quad setup when I was in the Navy, 22 and single (money was burning a hole in my pocket).I was in the Philippines, and the Navy Exchange price was low. As an example, the Akai speakers were only $60.50 apiece, so 4 of them didn't break the bank. Anyway, a year and a half later most of my stuff was stolen. So thirty -five years later I discover all this vintage electronics in the on-line auction site. So I have replaced everything that I had (except the 8-track tape deck)and restored it. Nostalgia, you know? First good thing I ever bought with my own money. I love to play it, but I do not have much quadraphonic material to play. I have five CD-4 LPs and one SQ LP. But I like playing any good music through the four speakers on vinyl. The other problem with quadraphonic is they only made those records for about 5 years, which greatly limits the selection of music. But you can play stereo through the matrix decoder and get a simulated surround sound, so it's somewhat useful.
I might have tried to replace the tape deck(Akai CR-80D-SS)too, except it was so good it has become a somewhat pricey collector's item. Hope this has been of interest.