I own the STA200 and imo, there is not much a better amp suited for a passive pre. For giggles, I hooked my SYS to it directly, plus my Pro-Ject Prebox s2, and the sound was fantastic and quiet. I do prefer my RP-5 which seems to add a little bit of warmth and 3d (just a smidge).
I'm curious about the Vidar. Plus, the Class D PS Audio Stellars