Here is what CC Poon wrote back to me about incorporating the NM24 into an existing HT system with receiver/processor:
"The easiest way is to feed the L/R 2-channel signal from your 5-channel decoder
(the HT Receiver's front L/R out) to the Line Input of the M24.
The front panel button of the M24 will allow the front L/R signals to pass
through its internal tube Line Amp gain stage(abou 16 dB gain)
to the Output, to drive the two channel power amp/speaker system."
No mention of an HT bypass feature, but I guess this will work for my purposes. This is a really neat product!