I think you'd have to put a stereo DAC on there (well, it'd probably cost less that way) as the centre & sub are on left & right of that stream if configured appropriately. There's something like a 4th order low pass for the sub output, and the level would all be adjustable in software - all that'd be needed is a buffer opamp to (a) protect the dac and (b) give a decent drive level.

Hugo