Mike,
I wanted to buy your KXR, I really did but I just bought the MX-Rs and that's too much at once. On the subject of BAT preamps, I've found them to work very well with solid state amps. I've used the VK 5i, VK 50se, and now the VK 51se over the past 11 years with a Krell FPB 600. I don't have it set up yet but very soon I will be using my VK 51se with the MX-Rs. I can't say for sure yet but I have no doubt the combination will work very well. I'm switching to the MX-Rs because they're considered a great match for the Vandersteen 5As. If you're curious on how this all works out, I can keep you posted. I plan to use the VK51se with the MX-Rs until I can comfortably afford a KX-R which may be a while.