I remember seeing a really clever trick for getting different behaviour between 2.0 and 5.1 back when RCA plugs/jacks were used for carrying signal between DVD/BR and AVR... will try to remember what it was.

Then again all that is probably gone now that everything goes through HDMI...

M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8