If this question is from Mr. Tim Whyte, then I doubt I can enlighten you beyond your already extensive expertise. Dunno about those "well-known" tweaks; wasn't aware of that. However, I did some home-brew upgrading in my old Phase4000 via replacing cheap stock resistors with quieter metal-film versions of the same values; it did quiet down the thermal noise significantly. You could also upgrade the caps to Nichion's etc, although I didn't. I wouldn't spend a bundle on Black Gate's or Vishay's though, the equipment just isn't that great IMO (I sold mine long ago). Internal wiring can of course also be upgraded. Adding an IEC power connector (& scrapping the captive stock AC cord) would probably be very worthwhile too. Have fun!