Fix Aesthetix Io volume control?

Yes this is more complex for you to fix.
If there is no sound from it.
If it's switched resistor (series/shunt) volume pot then it could be either the wiper series resistor is not contacting or you have a dry joint on the input output or ground wires.

If it a switched resistor (ladder network) then you could have one resistor that has gone open or one of the resistors solder joint is open, also the input output or ground wires.

Cheers George

O_holter, about 7 years ago I had a crackling noise in one
channel of my Io as I rotated the volume control. My thought
was that something had gone wrong with the volume control. I
sent it back to Aesthetix to resolve and when Glenn got it
on the bench, it turned out to be a loose socket for the
6sn7 tube. He replaced the tube socket and I haven't had a
problem since.

Yes by all means O_holter, I thought you nailed the problem down to the volume control yourself, but yes if you are not sure, then Rushton has a good point to make.

What you should do is lift the lid to swap tubes left to right to see if anything changes, or very slightly wobble them and listen to see if you get noises or music coming back.

Cheers George

less likely the resistors in volume pot will go bad. connections to those resistors is actually culprit

Honestly do want to try your luck on this level of equipment? I wouldn't if you don't have good component level electronic trouble shooting skills.

This isn't your typical PAS 3 open for experimentation . You could potentially make a mess of it.

I can think of a number of scenarios where faulty connections on the VC may be suspected but would be far from the truth in terms of symptoms.

Find an authorized tech -you're getting arm chair advice from some that don't even know how sophisticated the VC contro really is!

I'm educated in EE and I would rather not touch mine if I had concerns, I don't have the prints and even if I did I'd have to float around between the print and PCB to familiarize myself. The 2nd one is always easier to repair when you learn on the first!

Good Luck