I have a pair of Vienna Acoustics Strauss and a BAT VK-50SE preamp, as well as a VK-D5SE and VK-P5. I'd recommend a SS amp, FWIW. In my experiences, the bass on the VA's drops below 4 ohms, remember 4 ohms is the average impedence. I don't feel that a tube amp can control the woofers you have, bass will be under damped and soft.
I just sold my Clayton Audio M100's which were perfect mates with the VA Strauss, however, I found they didn't mate so well with the preamps that I liked (mostly tube variety). I've got a Blue Circle BC 204 on order, this is a hybrid design. I considered a BAT VK-75SE and a CJ Premier 140 (as I also currently have a CJ 16LS mk II preamp). However after talking with many Strauss/Mahler owners, and trying a VAC 100/100, I realized that a tube amp would not cut it with these speakers.
The BC 204 has a tube input stage and a SS output stage, and is fully balanced. If it's too expensive, maybe you could try a BC 202, or look for a used Threshold/Clayton/Rowland. I've found these amps to work well with VA speakers. I owned the original Beethovens before I upgraded to the Strauss a couple years ago.
Happy Hunting,
John