I tried to pull the knobs off, but some seem like they do not come off. The Master Volume, Browse, and Type knobs seem like they are not designed to be removed.
The ones I did get off measure 1/2" diameter for the small ones, and 3/4" diameter for the larger ones. Both have a 1/4" d-shaped shaft.
I'm too chicken to really pull harder on the knobs I couldn't easily remove. I will probably not replace any of them since I can't replace them all. Kind of a shame because I think some higher end knobs would have a better tactile feel and look pretty cool.