what impacts the sound quality more amp or pre-amp

It's about interface with the surrounding components. The pre needs to have enough of the right inputs and outputs, perhaps be able to handle your given cartridge(s), have an appropriate output/volume control and output impedance for the amp. The amp need to have the right input sensitivity and input impedance for the pre, and the right power output and impedance handling for the speakers/room, and perhaps the appropriate output taps and number of binding posts, and oh yeah, they have to sound good together! With all that said, and being in complete agreement with Kurt, and though you'll probably have more hands on with the pre, IMHO the amp is usually more important.

Dvdgreco, if your looking for advise on the best bang for your buck system improvement, why not post your system? Be careful of advise touting personal technology preferences without considering your personal budget and system.

My memory could be failing me on all this, I could be mistaken, but if I recall correctly the B&K's ST series, had a rather low input impedance, and a low V input sensitivity for full output. Both of which can make matching a tube pre to a bit tricky. Another concern might be the ability of the B&K's non + ST series of amps ability to handle 4 Ohm loads well.