Ah, I misread your post. I'm not that familiar with your particular setup, altho many years ago I briefly owned one of their first acoustimass sat/sub things I got thru a buddy who was doing a deal with Bose in setting up a system for his father's bar/restaurant.
I just took a peek at the manual for your gear. It appears to use the amp's speaker connections to the sub module with a special connector then distributes to the speakers from there with even more special connections but appears to get LFE signal from the avr's subwoofer pre-out. This pre-out connection is still there, both the avr and your module thingy is plugged in? Is the volume adjustment for the sub changed? You still show in your avr you have a sub connected and have tried the avr's sub volume control (trim adjustment)? You only are not using the center speaker special connection from the module thingy and disconnected the module thingy's connection of the center channel from the avr? Maybe these are set up weird, but I'd think you should be able to do that, don't see any thing in the manual addressing this situation, though. You might confirm, even with a photo, your connections (all of them).
Next time, buy real stuff, you'd be amazed at what you could buy for this price and how much better it would sound...
"I realize that somebody playing free music isn't as commercial as a hamburger stand. But is it because you can eat a hamburger and hold it in your hand and you can't do that with music? Is it too free to control?" - Don Van Vliet (aka Captain Beefheart) discussing commercial success in the music biz