I'm trying out King's Quest VI in both ScummVM and DOSBox, and the music sounds better in DOSBox. For example: the channels are much more crisp and pronounced, the instruments sound more realistic, there's substantially more bass, and the fades are much more prominent. The sound effects are also more realistic: using a door produces a reasonable latch/slam sound effect, whereas ScummVM only manages a simple bloop.

In DOSBox, my INSTALL.EXE config is "Sound Blaster / AdLib Card (or compatibles)" for Music and "Sound Blaster" for Audio, and my DOSBox audio config is the default. In ScummVM, I tried all of the Music Device options. Pretty much everything except Windows General MIDI (which is closer, but not the same) and MT-32 (which is just a totally different sound) produces the same kind of audio. Is there a setting I'm missing? Why does DOSBox sound the way it does?

   

For sound effects: Try checking the Mixed Adlib/MIDI checkbox in the ScummVM audio options. This selects digital sound effects in SCI games when it is checked, otherwise MIDI effects are played instead (this option will most likely be removed because it is confusing - it'll return in the future in a more user-friendly option, when the GUI supports it).

For MIDI music: Known issue, there is a bug in the SCI music code which results in some instruments missing, thus the music sounds a bit more "flat" in some games, like King's Quest 6. Nobody is working on it right now, though

   

The sound effects toggle has been removed in the latest unstable version and the upcoming 1.4.1 version. In the meantime, you can use a daily version from buildbot:
http://buildbot.scummvm.org/builds.html