A lot depends on what ones expectations of "passable" is. Small size means small bass. Assuming you're planning on using a subwoofer (That Bose system you mention uses one), then the lack of bass shouldn't bee that much of an issue.
So, what is it that you find objectionable about your brothers speakers?
Personally, for standalone "full range" speakers (not depending on a subwoofer), I find that 6 1/2 drivers are the smallest I would go. Now, adding a subwoofer is another matter.
If you don't mind a subwoofer, then this system has my interest. The reviews are outstanding.
http://www.svsound.com/speakers/prime-series/prime-satellite-5-1