Hi, I am using the 1k card. I never tried anything different, my dealer has a VPS and a Skala, he just set it for me and I've loved it ever since.
I do seem to flip back and forth from tube gain only to tube + SS gain. The tube only a little more transparency and beauty, with SS a little more grip. Kinda depends on the music and my mood. Both are very good. (My preamp has tons of quiet gain)
Also, if you read the manual, there is a symetrical input option. I guess it somehow floats the ground. This is something I want to try to see if it has any effect. Have either of you experiemented here?