it's your preamp that needs HT passthrough, not the HT Processor. What the Passthrough does is take your front L/R outs from your HT pre/pro into your stereo preamp which sends it to your front (Joule) amp. If your preamp doesn't have passthrough you can use a spare input from your preamp for this purpose, but its less ideal.
Your notion of driving your Avalons with 2 different power amps and switching between them is the least ideal way of all IMHO.
Your notion of driving your Avalons with 2 different power amps and switching between them is the least ideal way of all IMHO.