Piece of cake. I do this on live recordings, and THERE the drift can be BAD. I have to go section-by-section.
But your Tyros probably is just a bit slower.
 
Does the song end at a definite point or does it fade out?
 
If it ends at a definite point, trim the end of the clip to be exactly on the end of the last bar. Even with all of the autoaccomp playing at once, the downbeat should be clearly visible. Go one bar beyond that.
 
Next, if the Tyros is slower, shrink the track. If it is faster, stretch the track.

I think you are saying it's in time and then over a short period of time one tempo will change causing the whole thing to go out of sync. A simple stretch will only work when the tempo difference is constant.

It seems to me that either Sonar is "hickupping" or the Tyros is. Have you tried playing with the Tyros for an extended period of time, listening for hickups?
How are you monitoring when you're recording? Through Sonar or directly from the Tyros?

If that really is the case it's time for the repair shop I'm afraid.

Let's see how much your Tyros' timer is out by.
 
This assumes the Tyros clock is running slow or fast. If it really is fluctuating, this won't help much.
 
1. Find the simplest beat you have. Best a rock 4/4. Set the rhythm to 120bpm.
 
2. Record 17 bars.
 
3. As accurately as you can, trim the beginning to the first bar. Zoom in as much as you need.
 
4. Visually count across 16 bars, zoom in to the first beat of the 17th bar and put the Now cursor on this first beat.
 
5. Go to Project > Set Measure/Beat at Now...
 
6. Enter Measure (17th measure) and beat (1st beat)
 
7. Hit OK and the beat displayed in Sonar is the actual tempo.
 
For more accuracy, record more measures.
 
If you have access to an electronic metronome, set that to 120, start both and see if the one catches up and passes the other. Could be the electronics in the Tyros is faulty, although it really should have a crystal, so that is worrying.
 
 
 

Okay: just to make sure... I am looking for the first beat of bar 17? (Yes, I will never win an award for musical brain of the year).

Yes, although Sonar may suggest 16 beat 4 by default.
 
I am saying use beat 1 of measure 17 because that will probably be easier to see in the audio.
 
If you can see measure 16 beat 4, by all means, use that.
Just so long as the position of your cursor and what you tell Sonar is the same.
 
I have to shut down now, I'm sure you're fine from here.

I have also played the Sonar metronome and the Tyros metronome simultaneously at 120bpm... and I'm afraid that the Tyros soon starts to lag behind.
Will Yamaha be able to fix this?
 

I've googled a little and found some user reports. One person said that if he had to many things in "USER" this started to happen. Another thing I figured is that perhaps your tempo controls are a little corroded and the tempo dial or "tempo down" knob may be triggering erratically.

Hi to whoever might still be prepared to tune in.
I did a factory reset, have got the Tyros up and working, recorded a basic style at 106bpm with the X1 metronome playing at the same time.
All sounded great, until - bizarrely - 1min 13 secs (again!) when there was a noticeable loss of sync. Brand new project, brand new everything.
How can this even be possible?!?
HELP!!!!!!!!!!!!!!!!!!!!
Mark
 

You should probably at least take Sonar completely out of the equation. If you don't have a standalone metronome to test with, just google "online metronome" and test with the first several in the results list. Make sure nothing but your browser is running while testing, and see what the results are. If it still drifts, at least you'll know it's not some kind of interaction between Sonar and your Tyros. I don't know how good the online metronomes really are, but if you check with several you should get some kind of idea what's going on.