Hi,
Great to hear from you! On the ICs I would be very careful, we went to a lot of work to make the circuits work with 5534s (which are pigs of devices in many ways, they love bursting into oscillation) so any other ICs might well behave...not as you'd expect. Unless you do a lot of work around them. And anyway any audio problems with the 5534s are swamped by the switching FETs and the VCAs!
That said, it's certainly worth checking if any of the 5534s have gone noisy, and replace them if they have. It's usually pretty obvious if they have.
But the capacitors can definitely be improved, many of the coupling caps are really too small in value compared to what's available now in the same size packages, hopefully others here can pass on what they've found works well.
Best upgrade for the sound if these have '11 and '12 cards in is to replace them with '293 and '294 cards, these make the FET switches sound much better. But of course that can be quite an expensive mod unless you're lucky!
And of course fit a '291 input card. But I would say that
Actually that's more down to what you like the sound of.
Keep us posted! And look forward to seeing what others come up with.
Cheers,
Andy
