Took a little trial and error but got 6 channels happening last night.
Looked at movies in cue on my DVR and more than half of them are 1930s-1950s so not much surround or sub happening.
Best of my unwatched short list for sound effects was "snow white and the huntsman"... Looking at the meters on my puny amps, lots going on in the surround channels and more sub activity than other movies so far. One Steve Segal movie was disappointing for sub output.
I was correct in my estimate that 6x 10W would be louder than 2x 10W
The decoder puts the mono dialog channel and sub channel on the same stereo output cable so for now the sub output is just tickling the meter to keep the dialog channel at a reasonable level.
Since I was selling surround systems (my delay based kit) back in the '80s it is impressive how much surround has been refined. Dialog shows up as full center with L/R front -3dB to -6dB (guess based on meters). Pure surround is almost all in rear channels with just a little in L/R.
It probably shouldn't be a surprise but late night talk shows put the audience sound completely in rear surround channels. I expect sports like baseball games will do a similar mix routing.
I wasn't brave enough to put my 50+ year old AR4X in the dialog channel since it is doing the most work, but I do need to see if it still plays. For now I am using a few of my small computer speakers for the two surround channels and center dialog.
I worry that this may reduce my enjoyment from watching old mono movies. In my old surround sound kit I had a stereo synthesizer mode where L+R+delay fed one side, and L+R-delay fed the other side. The delay caused a comb filter with different notch locations for a sensation of stereo... Maybe we need a modern version of that.
The (very cheap) surround decoder has a weird start up ritual. If I turn it on from the power strip it locks up in some mode with all input lights on and no sound. The selector switches are unresponsive. The only way it works is if I unplug and replug the power jack at the decoder (perhaps a start-up processor boot up quirk). For now I will just leave it plugged in 24x7 and switch the three power amps with the power strip. Before I got the decoder working I had some momentary distress, "how do I troubleshoot and optical input???" Luckily for me the old school unplug it and power it up again worked.
I'll be dialing this in for a while but already night and day better than before... continuous improvement.
JR
PS: I am leaning toward using my two 6" 2-ways in series for the center channel. Running them at 16 ohms should improve the sub balance and they are my best sounding vocal range speakers. The 8" 3-ways could be L and R front speakers, and I'll use small computer speakers for the rear surround speakers. (I have 8" surround replacement kits on order because the 8" surrounds are going fast).
PSS: Funny how "surround" has two different meanings based on context here.