My previous mixer had unbalanced inputs, because it was really a keyboard mixer. In my defence, it was what I could afford at the time! :-/ So I found out all about power supply noise and why balanced inputs are a Good Thing...
Anahata, the first-draft version is just using ye olde TL074, I'm afraid. Cheap, easy to get hold of, and reasonably low THD if I make sure it's not driving low-impedance inputs. Nowhere near good enough for production though, of course, but fine for experimentation! A more serious version will be using 5532s or 5534s as a minimum, or maybe some more exotic variants if testing shows real improvement, and I'm going to replace the TL074s with 5532s (on adaptors boards) anyway on general principles, now I know that things work. For the final version, improved THD over the 5532/5534 isn't as important to me as improved bias current, so a fancy new JFET one that hits all three major food groups (low bias current, low noise, low THD) would be worth it. I know Burr-Brown for one keep throwing out ads about their new designs, but I've not kept up-to-date with what's actually around right now.