I've actually done a little digging, and it appears that the 1957 release of the soundtrack....
...Doesn't suffer from the same problems as later releases. I've listened to rips of this old stereo release, and I have to say, if somebody managed to get a hold of a clean copy, the sound is very full. It doesn't have the overly scrubbed sound the home video releases have. In fact you can hear more of the instruments. The instruments all sound pretty good.
Some guy on youtube was working on a restoration of the film to bring back the true fantasound. He claimed he used this soundtrack and a mono mix (where he got that, I haven't a clue). He disappeared off the face of the earth, and his video on the process has been removed. I have it archived on my drive.
I'm sure there was some slight audio trickery involved in the soundtrack, because I hear subtle reverb, but then again, I've only heard the soundtrack scrubbed to death of any high frequencies. It was common practice in the 50's to electronically reprocess sounds and they'd also add reverb to fake stereo. It doesn't sound that extreme.