Thanks for the reply. I'm mainly looking for clarity. I would think that's related to slew rate for transient response as well as thd and noise. When I changed out the op amps in my Bellari Preamp around 10 years ago, it made a tremendous difference. I chose that based on some other modder's suggestion who said it was lower noise and faster than the originals. So, lowest noise with highest slew rate is maybe what I'm looking for. I'm not sure what amps are in the Pro VLA II since I'm not near mine, but I know they are replaced in mods by Revive. I will have to put a socket on the pcb so I can try out different flavors. I was thinking about also upgrading the op amps in my Bellari while I was at it, right now it has the AD823ANZ dips I put in there a while back.
I really am just looking for suggestions on more recent op amps that I may try in these items. I know it's time consuming to burn in the op amps just to see if it sounds ok, but that's my plan. They're both 2 channel devices, so it will be easy to AB.
Is there going to be a different operating impedance for the different circuits, or is that a standardized thing? If not, I should be able to get the impedance specs of the existing amps, maybe? What other specs should I pay attention to as far as making sure it will even work in the circuit?
Edit: I thought I'd come back to say that you're saying that I should choose an area to improve upon, but in low cost prosumer gear there ARE general upgrades that can invariably improve the audio path like replacing the cheap caps with Panasonics and popping in higher quality op amps (if you know how to chose the right ones).