I use both tube and solid state BAT amps in my system along with a D5 and 5i.
The strengths of BAT SS amps are probably obvious to you, since you own one. They don't offer the typical 'personality' associated with most SS amps. They aren't etched, glassy or grainy sounding, but neither do they present an airy or 3 dimensional quality. IMO, they certainly lack that good ol' tube magic, and rightly so. I use a VK200 for the bottom half of my biamp rig.
The VK60 suffers from a bit of bloat. It does't render low frequencies as well as a good SS amp can, but the realism & rendering of individual performers in space is very engaging and the upper frequency extremes are sweet and delicate. In short, the midrange is to die for. For female vocals(one of my weaknesses), there is nothing better than a good tube amp, and this is one of them. As you can probably guess, I use a VK60 for the top half of my biamp rig.
If I had to choose between the two, given my musical tastes, I would choose the VK60 hands down. I can live with less than perfect bass performance.
In my limited time listening to the VK75se, I got the impression that there would be much less of a trade off between the two design types. YMMV...
