BAT or Pass With My Sophia 2s?

I have both: a pair of Pass XA 100.5 monoblocks and a VK-600SE.

My speakers are Wilson Sophia 2. Preamp varies between SS and tubes (I'm still searching...)

Both are great amps. The differences to my ears:

Pass:
- Better midrange
- Thicker, more tube-like bass
- Warmer presentation overall, not much in the way of 'air', but highs are very smooth

Bat
- Bass is much tighter, less overhang
- Midrange and highs not as smooth as Pass
- Leaner presentation with much more air

At the moment I prefer the Bat, but both amps are great.

Meant to add that if you're going with a tube pre, the Bat would be the one I recommend.

Madfloyd - thanks for sharing your impressions. Thinking of going VK600SE and Rex preamp. Any experience on your end with the Rex?

Consider Madfloyd has not yet paired his Pass Labs XA-100.5 with a preamp that matches optimally (the preamps he used both have high output impedances that are too high for the Pass Labs amp). This is based on his comments in another thread.

So, take his recommendation here with a degree of caution.

From a thread discussing Pass Labs XA-30.5.

06-13-10: Madfloyd
I haven't had good experience driving the Pass with tube preamps. I've tried the Cary SLP-05 and the Audio Valve Eclipse and the low bass is rolled off. It's one of the reasons I got the Bat.

Both the Cary SLP-05 and Audio Valve Eclipse have output impedances that rise to 3400 ohms and 3090 ohms at 20Hz. Not good when matching with an amplifier having an input impedance of 20k ohms/30 k ohms (single ended/balanced) as does the Pass Labs XA-.5 series.

Match a tube preamp with a low output impedance (below 300 ohms, IMO), and you will have an excellent match with Pass Labs XA-.5 series amps.