I've tested all of those and
Only Sonic 2 has stereo in coins/jump sound, no other sonic games by aspect or other sonic 2 sounds have stereo effects (at least the sounds/music i've heard)
No Outrun or Outrun Europe has stereo sound (at least the sounds/music i've heard)
And X-Men, Oasis, Galaga and Aleste yeah, they have nice stereo music/sounds
Here is some peak analisis
Galaga
http://i54.tinypic.com/11h6oux.gif
Oasis
http://i53.tinypic.com/2hgv33p.gif
Sonic 2
http://i53.tinypic.com/33onn2t.gif
Aleste
http://i53.tinypic.com/foes1c.gif
X-Men
http://img861.imageshack.us/img861/1773/ezmen.gif