I'm not sure just how "stereo" the new pins are with their music/speech/effects sounds, but at best case it's just 2 channel stereo.
Most earlier machines are simply "dual-mono" fed into 2 speakers on the headbox to look like it's stereo....marketing trick.
For full surround effect you'd need 4 (well, 5) individual audio channels within the pinny to bring them out externally.
While modern pins have multiple audio tracks within them, they're digitally mixed converted as a mono/stereo output to the speakers, so there's no real way to get to the individual soundtracks.
I made an addon mp3 FX board for a pinny long ago, and since then was asked to make it into a surround system which was easy to do as all the sounds/synthesis were increased by adding more chips for the extra channels.
MM
