Since instr.dat (of Altered Destiny) contains three sections: Adlib, Roland MT-32/LAPC-I and Casio CT-460, I doubt your version. Seems something is converted into Adlib, MT-32 and CT-460 compatible data, thus that something would barely be already MT-32 compatible. PC speaker music is usually stored separately, because of only one voice supported. Some driver systems (Miles AIL 2.0 and 3.0+ among them) allow playing MIDI data over a PC speaker, but the result is highly unpredictable since one voice is played while others are discarded.
In Altered Destiny setup program, you can choose from PC Speaker, Tandy (I believe 3-voice one), CMS and MIDI. For MIDI, you have three options: Generic, MT-32 and CT-460. Selecting Generic, you hear only piano music (it is so intended, according to the help files). Also, Generic option is absent from instr.dat file; thus, we can assume that MIDI music is stored in a 'Generic' format where all tracks are piano or none; being converted for Adlib, MT-32 or Casio CT-460 when such option is selected in setup. PC Speaker, CMS and Tandy music seems to be stored in some other format(s).
Hardware comparisons and game system requirements: https://technical.city