Problem with GUS under dosbox0.72 is that dosbox doesn't come with all the needed GUS drivers and doesn't initialise GUS at start up. That's why you better stick with SB emulation.
SB emulation is nearly perfect in dosbox.
First possibility: disable GUS in dosbox.
Open dosboxconfig and look under header [GUS], change gus=true to
gus=false, this will disable GUS autodetection and you will be able to select SB sound.
Second possibility if you absolutely want full GUS support:
http://vogons.zetafleet.com/viewtopic.php?t=16974
Read and apply, this will give you a fully working GUS emulation under dosbox 0.72.
However, some games that can use GUS sound are sometimes nitpicking and this will cause those games to freeze, but it should work for 99% of the GUS supported games.