You cannot use Bose cubes without the Bose Acoustimass. You didn't say what kind of 7.1 system you're talking about. Is it some other Bose system or just a 7.1 receiver? You can go from a receiver to the Bose Acoustimass to the cubes. So, you can use your Bose Acoustimass 5 for two channels from a receiver. You might be able to run two wires from a receiver front center channel to the two Bose Acoustimass in's, then two wires from the Bose Acoustimass out's, one each to the two cubes. Seems like that would work, maybe.