The original Broadway production opened in January 1988 and had not recouped by season's end. It did recoup by end of the following season. (They did not make specific announcements back then. Just the annual season tallies in Variety.) I remember reading that the show would need to sell out 40 weeks to recoup and it did sell out week after week.
There were no outside investors. Show was produced by Cameron Mackintosh and the Really Useful Theatre Company.
Cast albums are NOT "soundtracks."
Live theatre does not use a "soundtrack." If it did, it wouldn't be live theatre!
I host a weekly one-hour radio program featuring cast album selections as well as songs by cabaret, jazz and theatre artists. The program, FRONT ROW CENTRE is heard Sundays 9 to 10 am and also Saturdays from 8 to 9 am (eastern times) on www.proudfm.com