The problem with CSR (besides the synthesized music of course) is that none of the performers were in the same room. I am not sure what you mean by "the synthesized music" since this recording, rather famously, uses the 65-member Philharmonia orchestra (40 strings!) plus the 6-piece pit band from the London production.
When this set was released in 1988 music and theatre critics marveled at how the performers sounded as if they had all been in one room.
Of course, this SHOULD have been done with the Broadway cast. By the time the show opened in New York it was already an established hit and since Colm Wilkinson was repeating his now-historic performance, Gefffen should have release the complete show on 3 CD's and a single CD of highlights. Instead they chose to record essentially the same abridged version that First Night had done with the original London cast.
The CSR is at least a partial Broadway cast with Gary Morris and Tracy Shayne recording the roles they were playing at the time the recording was made. Morris was most impressive on stage as Valjean, although Wilkinson more or less owns the part. (Wilkinson last did the show - I believe - in a special 6-month engagement in Toronto in 1998.) It's really nip and tuck between the two.
For me, the CSR is the most satisfying listening experience of all the LES MISERABLES recordings.
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