Hi, So I've owned a VK200, VK 60, vk75SE and 150SE's over the years.
I'd say jims comments with the VK 60 vs SS were right. I actually like the midrange glory of the vk60 over the vk200, but that's just a system matching/taste thing not a differing opinion.
The 75SE dramatically adds extension and weight and makes this a tougher choice with current models. Also seriously drops the noise floor over the vk60, it's much more ss like but keeping the tube warmth in mids.
Also, the SS amps sound best left on, takes a few days to get the best sound. Of course tubes do fail. So pick your choice here
In the end, I think the 75SE will yeild more midrange magic. Room size, speakers, cables, your tastes are really the things to consider also here.
BAT makes good amps.