I have the MGM DVD. It is a nice transfer (even widescreen!) possibly from one of the original movie reels but I think it is a sort of simulated stereo (was there stereo in 1969?) Anyways, the sound seems slightly low and subdued. I never really noticed the music till your posting.
It'd be great if they re-released a digitally cleaned up and sound seperated version of this classic which I would re-purchase based on your posting!