I don't know if DosBox by default emulates that or not, but when I played Yendorian Tales Book I Chapter 2, it required an old Soundblaster driver called
sbfmdrv.com to be loaded into memory with Ms-Dos / Windows 95's Ms-Dos ver. 7 as a resident driver.
You can get that attached archive
here which contains that file, then try to install it in DosBox by typing the command
loadhigh sbfmdrv.com (got to have that file in the same folder as the game), or probably simply type
sbfmdrv as it's a self-running exe file, before starting the game (or add the line in dosbox.conf file to do it automatically at each DosBox start) and see if that helps.
P.S actually I do remember that I've been briefly trying out the game above in DosBox some years ago, and had also to install that driver for the sound / music to work, so you probably
do need it.
As The Tyrants of Thane is the following-up game made by the same company, it probably needs that driver as well.