Recording with midi; end recording out of sync

I'm having what I assume is a latency issue that I need your help to resolve. Quite often I'll assemble a Sonar project that has a few audio tracks and one midi track (usually the melody) that I use for a practice backing track which I play along with as I record myself (for later analysis). (All tracks made originally in Band in a box.) As is, these tracks when played in Sonar sound fine. My problems comes about when I add another audio track to record myself playing along with the midi melody track. I've discovered that when I play back the recording, my playing is out of sync with the midi track, yet I assure you it was spot on as I performed and heard it in my headphones. If I convert the midi to audio and then play along while recording, the out-of-sync issue disappears. So, I guess I'm experiencing some sort of latency issue with midi? FWIW, my system is Sonar X1 Studio, M-Audio Fast Track Ultra USB interface, into Win7-64 16GB coreI5 computer, midi is routed to a Ketron SD2 sound module. Again, the question boils down to: Why is the playback out of sync?
 
I appreciate your thoughts and suggestions. Thanks!
 
Bob aka jazzwombat

Thanks for your reply.
1. How is the audio of the SD2 integrated with the Sonar audio during playback & during recording?
>> Midi In/out thru FastTrack's channel 5/6
2. External mixer?
>> None
3. Sound card input? (Fast Track Ultra)
>> Inputs are mic to channel 1, midi in thru 5/6. Not sure of your question, sorry.
4. About latency: are you using effects on your audio in Sonar? Are you avoiding the latency-inducing effects (e.g. perfect space)?
>> Problem occurs with or without effects in place
 
I'm not currently at my audio workstation, but will provide a more detailed description of the hardware connections between the audio interface, SD2, and computer later today when I examine my setup.
 
Again, thank you.
 
Bob

1. The midi track you already have in Sonar: does it drive the SD2 or a softsynth?
>>It drives the SD2 whose output goes into Fast Track 5/6.
2. Does it then go into Sonar and get mixed there with Sonar's other audio and come back out through the Fast Track to your speakers?
>> Yes. The SD2 goes back into Sonar other audio and comes back out thru Fast Track to my headphones/speakers.
3. What audio are you recording?
>> I'm recording my sax thru Fast Track input #1 (front mic jack).
4. What buffer size are you using in M-Audio?
>> 128, which I think is as low as the driver version I current use let's me go.
 
I discovered that Avid who bought the M-audio interface line has a new driver that suggests some corrections with latency problems. I plan to remove my current M-audio driver and install the new one later this week (weekend) to see if this corrects this problem.
 
Anything additional you wish to suggest is appreciated, and thank you for your time.
 
Bob