delay between audio and midi tracks

[weezerboy]

im having a problem when i record midi tracks in a session that already has audio tracks. say i record some guitars and then record some midi drums and then quantize the drums, the drums are significantly behind the guitars. if i change the buffer size, then the lag between audio and midi changes as well. i have the midi playing out of pro tools through my yamaha s90 and back in to pro tools on an aux track. im using 6.9 on a g5. i know there is no delay compensation in pro tools but i didnt think that would cause a problem with midi. if i do a whole session with just midi everything is fine, and if i do a session with just audio everything is fine. if i mix both in one session i get this problem. if its not possible to use midi and audio together in LE, then that pretty muck makes LE useless to me.