"The slow compressor can be made more useable by changing one 2.2uF timing
cap to 0.47uF which makes the attack & release four time faster and the
compressor much more usable."

Is it something I could do myself? I'm handy with a soldering iron but not
much experience inside a preamp.

If you can find the right cap, it should be pretty easy to replace. I doubt
you'll find many 2.2uF caps anywhere in that unit, so it shouldn't be too
tough to track down.
BRBR

You should call Avalon. I bet they'd do it for you and be glad to know there's
a way to make their mediocre compressor better, assuming they are even aware of
our low opinion of it.

In my experience, they are very congenial and open minded.

-R