Dana, good to hear how you're enjoying the surround sounds from your QS8s. Incidentally, don't limit them to "multi-channel music"; the surround effect is excellent with 2-channel source material in ambience extraction modes such as DPLII.
Yes, for the type of sounds sent to height speakers, very wide dispersion, as provided by the QS4/QS8, is an advantage.
Absolutely John!
I have my Onkyo set automatically to convert all 2 channel material (TV/Netflix, etc) to PLII DSX, all 9 speakers serving audio bliss.
5.1 material is auto converted to DSX to all 9 speakers. My only exception is when listening to my flac music collection, it's set to "all channels".
But you are 100% correct, PLII DSX is magic for sure. Sometimes, I can't tell the difference when listening to 2 channel cable movie from a 5.1 channel cable movie...
Dana