But that would imply that "Surround 6" is doing genuine THX EX decoding?
Right, selecting "Surround 6" will give you THX EX decoding, assuming you have EX source material. I'm not sure what it does with stereo material. I use an outboard dac and "Direct" for all stereo source material.
Does the B&K Ref 30 have any DSP modes that support a 6.1 or 7.1 speaker system for std 5.1 DD/DTS discs, and especially DPL-only discs?
Sure. If you have one rear center, just enter "Surround 6" on your remote. If you have two rear speakers, enter "Surround 7" on your remote. Note: For THX-EX...