Carvin makes good sounding, reliable gear. I owned and used 2 of their PA heads/mixers on hundreds of gigs. My current PA is a complete Carvin system.
I've never heard any of their acoustic amps, but they do fit your criteria of having at least 3 channels and are portable. The S400D is more like a self-contained PA cab with 4 channels. Check them out.
http://www.carvinguitars.com/guitara...sticseries.php
BTW, they now have 2 new acoustic models which are not on that link, the AG200 and AG 300. They are in the new catalog.
Good luck.