While your suggestion that Pass amps have to be on 4 hours before they sound good strikes me as excessive, your mention of the stock power cord did cause me to try it. It was very enlightening.
The bass is more natural with the stock power cords. It's still thunderously deep and shakes my house causing any post 1970 acoustic bass to sound like it's mic'd and played through a rock concert PA system, but I hear some texture. On the other hand I don't hear any musical info above 8k (or at least that's how I choose to describe the presentation). I actually had to walk up to the speakers to make sure the tweeters were working. Do stock power cords need to break in too?
The .8's are powerful beasts. They can do rock really well. Switching back to my .5's they almost sound thin (although I can hear everything going on musically and it sounds open and airy). The Shunyata power cords help to thicken the sound.
Except for the time I've went back to my .5's I've had the .8's on night and day for a couple weeks now. I don't hear further changes although I'm sure they're still occurring - they're just subtle. I could see this amp being very helpful when someone needs to pressurize a large listening space.
I wonder if I should try switching the Shunyata Alpha Analog power cord in my preamp to an MIT...