I believe it's been discussed on AVS before, and IIRC correctly it will work if you connect the AVR's subwoofer output to one of the inputs on the Logitech unit (but I can't recall which one). OP, search this site for more info.
-- Edit --
See post #18 in this thread. (Note: The OP in that thread has an AVR with dual subwoofer outputs, which is why he talks about running two RCA connections from his AVR.)