Chris,
I used to own a VTL 5.5. I don't think there is a need to bias the unit. Certainly, impedance matching with the amplifier is an important consideration. I replaced my VTL 5.5 with an Audio Horizons TP 2.0nB because, apparently like you, I wanted the sound of tubes but also a sound that is well articulated and detailed.
At this time, I think there are better preamplifier choices for low wattage SET amps. That said, my TP preamp matches beautifully with my VTL MB 185s. Other users have reported similar results with other amplifiers (both tube and solid state). You may want to experiment by using the Audio Horizons free trial period. The Audio Horizons preamp can be purchased new for under $3K.