Here's the follow-up. I bought the Powersoft Mezzo 604A, which has 4 channels, a 600W power supply, DSP without FIR and auto-standby. I'm very pleased. It's a nice compact package that I mounted on the wall behind the TV with the business end close to one vertical edge of the TV so that it's accessible. It's super quiet both electrically and acoustically and, of course, sounds just fine. The auto-standby, which has a fixed -60 dB threshold, more-or-less instant-on and an ~30 min. hold, works perfectly. I'm using a miniDSP 2x4hd upstream for FIR filtering and remote-controlled preset selection (bass-boost on/off depending on program).
Thanks for the help, everyone.
--Frank