The MUSIC.PDM program in Deskmate 2 works in DOSBox with machine=tandy, but AFAICT it only supports Tandy 3-voice music and not the Tandy DAC.
The MUSIC.PDM and SOUND.PDM programs in Deskmate 3 use the Tandy DAC, and they work in DOSBox if you set things up in a specific way:
First, only a generic release of Deskmate 3 will work in DOSBox because the Tandy-specific releases typically require some part of the program in ROM. The generic releases don't include the MUSIC.PDM and SOUND.PDM programs, so you'll have to copy them and their associated files from a Tandy-specific release. I've successfully combined generic 3.02 with 3.02 sound files, and generic 3.05 with 3.04 sound files. I'm not sure how sensitive it is to mismatched versions, but it's probably a good idea to match them as closely as possible.
Unlike Deskmate 2, you don't have to use machine=tandy, you can use other machine types with tandy=on to have access to other video options.
Set sbtype=none in the DOSBox conf file. Tandy DAC detection fails if the sbtype setting is changed at runtime; it must be set to none in the conf. This also applies to the tandy=on setting if you're using something other than machine=tandy.
Lastly, a bit of general info about Deskmate 3: it uses the COMSPEC environment variable for the location of its config files unless told to do otherwise. If you're booting real DOS this shouldn't be a problem, but with DOSBox's internal DOS this means Z:\ will be used by default, which is not good. You could copy COMMAND.COM from the Z: drive to a writable drive and change the COMSPEC variable to point at it, but it's more convenient to set Deskmate 3's DMCONFIG environment variable. For example, if you have Deskmate 3 in C:\DM3, you would execute the command: SET DMCONFIG=C:\DM3
