I do use an external mixer most of the time. I never know when I'll have guest singers or the occasional instrumentalist.
I have a little bitty Behringer, a big Behringer, a Peavey and a Yamaha. They all work fine with it.
I leave the Bose flat (setting 00) and do and e.q. ing from the mixer. Most of the time I run everything pretty flat. It doesn't need much e.q. help.
DonM