A little question:
Some higher end Sound Blaster/Roland cards had "special sounds" which UFO used, like a police siren in the Intro as seen in link below:
https://www.youtube.com/watch?v=cuRzCHaeyXY
Can that one be added to OpenXcom, and are there other "special sounds" that UFO uses?
If you want the soundtrack that has things like the siren, you'll want the Roland MT-32 soundtrack. I don't think anybody's recorded it however, so you can't get it in OpenXcom yet. I can probably find someone at Vogons who has one to record it, though!
I could do a MUNT version until then, but that's not 100% authentic. It'll sound pretty close, though.