Thank you for pointing that out. I mixed up SQ6CD with KQVICD, which is SCI1.1 and uses 16-bit wavs.
Edit: SQ5 has an updated version of AUDBLAST.DRV that works with 16-bit wav files. Unfortunately, the quality through DOSBox still sounds like it's playing the 16-bit file at 8-bit quality, even after verifying that dosbox is configured to use 'sbtype=sb16'.
The 16-bit wav does sound better through ScummVM.