While a little unorthodox, my approach to this general problem (and to the fact that my old 565 could not bass manage correctly) was to essentially use speaker processors to do crossovers, bass management, etc, behind a 5.1 switcher preamp (Sony TA-P9000ES).
This has worked wonderfully. The P9000 also has a 2ch input for scenarios such as the above, and you also get the ability to add SACD players to the mix on a first gen 568 with this approach.
Read more details, and see a diagram of my rig at: http://www.mindspring.com/~jonfoulkes/BassManagement.html