There are no "black switches". There is a knob on the power supply that allows you to adjust bias, and a volume pot on the amp for headphone listening (and to adjust the level through speakers if you aren't using a preamp). The test points are in the back of the power supply for adjusting bias. I honestly can't answer your question regarding the 6V6/6L6 voltage setting, as I haven't used either of those tubesets (only 6L6GC and KT88). I would suspect that info is in the extensive build and design notes ... if not I can find out. I'm not sure what your question is exactly about the triode/UL setting. That was added by the builder to extract a little more power in the UL position. It's the toggle between the output tubes on the amp chassis.
Hope this helps.