anyone use the bat vk-75?

Avalon recomends for arcus amp in 30 – 150 W range.
At 75/ch of clear tube power I think you might get a great result with VK75.
Regarding Demo VK75 for $3k vs. Used VK60 for $2K, I would go with VK75. You will get non-transferable 5 year BAT warranty with it.
I would definitely try to compare it with hi quality SS amp at your house to see which sound do you like the best.
BTW, if you decide not to purchase this amp, please send me dealer’s name and contact number. I have a friend who might be interested.

I don't think the bat will drive the Avalon's well as they dip low in impedence and like current the bat don't have.

S2k, I can't say I've heard the vk-75 but just thought I'd mention that the Stereophile review found no difference in sound between the Vk-75 and the older Vk-60. I think you may get better value by either getting a single VK-60 for around $1.9k - $2k, or get a pair of VK-60s for about $3.5k.
Best of luck.
John.