BAT-VK31se or VK-50SE or LS17?

The VK31SE is NEWER and better and cheaper than the 50SE.

I have the feeling the 31SE may be better, but I noticed that the 31SE only uses 4 tubes, while the 50SE uses 8.

I used a BAT CK 30SE with my Classe CA-400 into a pair of Maggie 3.6R. I had to run the BAT up to very high settings on the volume control in order to get SPL's in the 90 db range. Assuredly this was partly a function of the speakers, but when I purchased an Audio Note M3 pre-amp, with choke rectified outputs the problem went away.

i had both---the 31SE clearly preferred.

I've owned the BAT VK-31SE, VK-50SE and VK-51SE as well as the Audio Research Reference 3. I'm not so sure that I agree the VK-31SE was better than the 50SE. The 31SE was more dynamic and powerful, but the 50SE had a more tube like lush midrange. I would say they were different, but I wouldn't say one was better than the other.The 51SE was able to combine the best attributes of both.

That being said, I also demo'd the VK-32SE, which I did not care for, and then bought the ARC Ref 3, which I believe is still the best preamp that I have owned to date. I haven't heard the ARC LS17, so I cannot comment.

Cheers,
John