bstspkr1: With the Pass X600.8 and Atma-sphere MA-1’s plus the pre-amps from both manufacturers, you are indeed dealing with quite rarefied equipment! Add-in your SoundLab’s and oh my! I’m sure you’re quite correct about trying to place either the amps or pre-amps above each other. Different is just that. It doesn’t necessarily mean as you said: “superior”! This can be said for much of the hardware at the levels many of us own.
I switched from CAT amps to Atma-sphere because of the CAT’s 190lb/ea. weight (MA-1’s 32lbs./ea.) and the need to replace a resistor that acted as a fuse for each of the 32 tubes in my JL2 amps. A tube blowing almost always equaled a blown resistor. I am disabled so having to get down on the floor to flip-over a 190lb amp and remove multiple screws and de-solder and re-solder a resistor was figuratively and literally a PITA! Otherwise, I would still own the marvelous CAT beasts (meow). I did audition the CAT’s against the Atma-sphere MA-1’s before purchasing the MA-1’s. There were differences, but neither was superior. So, it was painless opting to make the trade.
I would love to hear your Pass and Atma-sphere amps back-to-back. I would say in a shoot-out, but that assumes the selection of a winner. When bulls-eyes are hit by both, there is no win. Congratulations on what must be a fine sounding audio room!!
Did you audition or own other Pass amps with your SoundLabs before settling on the 600.8’s? If so, do you believe the 600.8’s are the pinnacle of the line when driving SoundLab’s? If you didn’t own the 600’s which other Pass amps would you select to pair with your U1PX’s?
Although I’m sure it’s difficult, are you able to make a verbal comparison between the Pass vs Atma-sphere amps with your SoundLabs? Is there one you find yourself using more than the other for sonic enjoyment reasons? I’m not generally a believer in using one component verses another for music types/styles (e.g. jazz vs rock vs classical vs vocals etc.) reasons. But perhaps your 600.8/MA-1 choice may be as such music style/type related as opposed to other traits. At any rate, having such a choice is a wonderful dilemma!!!