Sonar & DGX500

When trying to use a drum track for recording purposes from the Yamaha DGX-500, (only to use to record, let's say, a rhythm guitar alone) the tempo settings being the same (i.e.-100bpm), the Yamaha falls behind as I get into the song being recorded. I kinda understand the midi sync thing, but I'm not using the Yamaha as a midi device. I have the outs on the Yamaha going to channel 2 on the mixer as audio. Can someone explain the process to sync S3 and the Yamaha?

TIA!