I hear them in mp3s.
I've made my own approach to make these adlib tracks, and found one thing. Strangely, but DosBox plays adlib music in MONO mode, though, when port data recorded to disk (with ctrl+alt+f7) - it played with in_adlib in STEREO mode and gets greater quality. Another thing - version 1.2 have slightly different music format and files, other than from Steam. And I tried to use it, with kind of success. All 14 tracks recorded and encoded in mp3-128/mp3-160/ogg-128. Which is better?
BTW, "gmnewmar" music is not used at all. Not in original xcom, nor in openxcom (though it listed in loaded resources).