They sell a CD, I have it somewhere....
As far as MSHI goes, I've heard both the Matrix soundtrack and the regular MSHI soundtrack. On my last visit (this summer), I definitely heard both soundtracks playing in different areas of the island. It seems that the Matrix music is played near the Port of Entry entrance, and the standard MSHI music played from Spiderman to Toon Lagoon.
On a related note, I'd love to hear source music from USF and IOA. I don't know why source music from WDW is much more available than music from USF/IOA.
The "gong music" that is played at Port of Entry is not available anywhere. They do not play the Matrix music anywhere in the park, those are all from the CD. Around the Hulk and Storm you hear "Dr Banner Science Park" And around the Fantastic Four Cafe you hear some other track, cant remember it now.
You can find the CD on Ebay.
On a similar note, you can hear music from the Last Starfighter at the exit of Soarin.
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