Quiet passages have much more low level detail with the BAT. There is more texture overall. When the music gets complex and louder it gets the mushy sound.
Solid state warm up?
I recently Put in a BAT vk-250SE with bat pack into my system to power Dynaudio Contour S 3.4 speakers. I was using a B&K reference amp with pretty good results, but I wanted more detail and subtlety. I got both, but I also got a darker, almost mushy sound. Some material is worse than others. I have pulled the speakers a few more inches from the back wall which helped a bit. The sound may actually get better the longer the amP is on...hours. Could the amp just need to warm-up and maybe be left on 24/7? It does get quite warm. I use the 12v trigger to put it in standby. Any ideas?