These are the changes I put amps through: (1) The .1uf metallized polypro interstage coupling cap was my first stop. Doubled up to .22uf for starters, tried VTV silver PIO caps first, but ended up with Audio Note copper foil PIO's. (No cries of "Foul!" please. I don't distribute the parts. In North America PartsConnexion.com sells them.)
(2) In my case, the iron underwent a wholesale change next. (If I were to do it again, I might do the third step 2nd.) The parafeed OPTs were replaced by a pair of nickel MQ's. I upgraded the parafeed chokes as well, again with MQ's goodies. This yielded a spare pair of chokes which can be directly subbed for the big-ass 1.2kohm 10w wire wound resistors. A no cost upgrade which yields much smoother, more refined sound.
(3) The 3.3uf parafeed caps went next. Again, metallized polypro are not the nicest sounding caps, but they are cost effective. In my case, I scored a pair of Western Electric PIO caps from Mike Lefevre while he was in a garage-cleaning frenzy. ;-0
Note: Early on, I had subbed Black Gate caps into the PS. Heard next to nothing, which is assuredly NOT the case in other applications. The parafeed topology seems to minimize the sonic effect of PS cap choices. I wouldn't bother with them till I had run out of other things to monkey around with, if then.
Yeah, it's all been covered on the Bot Forum, but, as somebody else already said, "yer here, right?"