Bill,
Our guitarist has one of those ubiquitous cheap Behringer mixers with built-in FX and graphic EQ. It always sounds bad when we use it, but he insists anyway for the flexibility it provides. The mics he uses are dissimilar and very, very cheap, which obviously doesn't help, especially since they sound completely different and need EQ. The Bose has presets for different mics, but we can't use that when we use the mixer because we're feeding it one mixed signal (talk about mixed signals!). He's got a Carr amp and several expensive guitars (which he literally tosses into his guitar stand!), but doesn't really understand the concepts of garbage in = garbage out or weakest link as they relate to an audio signal, exemplified by the fact that he uses only the cheapest cables to connect everything (guitars, amps and PA) and they're always failing (he yanks on them, wads them up in a ball and trips over them regularly). Oi. Sorry about the rant...
If you use a small mixer, matched mics, good cables, watch your levels and leave all the EQ-ing to the Bose system, you'll probably get excellent results. It's an amazing little system.
John