Messing around with Goldwave and MKDD today, some extremely interesting results.
I tested this on "COURSE_CASTLE_0.x.32.c4", which is Bowsers castle.
I opened the sound in Goldwave and set the properties to;
Now after you do that, rightclick in the bottom lert corner where it says "Stereo", and change it to "Right". Now press the Delete key to completely erase the right channel, and press play.
It seems top be offset somehow, I'm going to keep working on this and see if I can find some settings that will work. I'm posting a link here to a WMA (Too lazy to install an mp3 encoder

) of "COURSE_RAINBOW_0.x.32.c4" (Rainbow Road) playing in Goldwave, notice a few things about it.
http://xce.et-mod.com/COURSE_RAINBOW_0.x.32.c4.wma
The pitch/tone is
exact as it should be. However, the offset seems to be constant throughout the entire song, causing it to be played in "pieces", making it play the main tune slower. I think there should be an automation function to correct the offset....somewhere