I was already a massive NIN fan so I LOVED the soundtrack. Even though I haven't heard it for years I can a) still hear it and b) picture the points in the game where it switched.

Trent Reznor makes great soundtracks. Natural Born Killers is incredible.

The Quake CD was some sort of hybrid data/music CD. It was possible to play the soundtrack in a regular CD player.

This was true of a lot of PC games from that time IIRC.

Yep. Basically the trick was to make one track as data, and the rest as redbook audio.

I seem to recall running into the odd album that was done up in a similar way to bundle images and such for fans.

Found the Wikipedia article on it btw, Mixed Mode CD: https://en.wikipedia.org/wiki/Mixed_Mode_CD