How to do multitrack audio recording (from an external sequencer keyboard) in Sonar 8

To sync any device to Sonar it must be capable of MIDI sync.
Read your manual for the Yamaha.
You will need an interface that has both MIDI and Audio inputs/
The other option is can it save and export MIDI files?
This would be simpler.
Some cheaper non professional keyboards are self contained and you are stuck with the stereo output. It is found that the sequences are not output to the MIDI jack.
You can drag tracks around in sonar to line them up, best to record a click intro.

Have you tried using the metronome?

You don't need a multichannel card to have audio play in sync, but you do need to perform it in sync.

You don't have to use the metronome, you could use the keyboard to give yourself a count in and launch from there. Then for the second track play along with yourself from the first take.

Edit: Noticed you said they're sequenced in the synth. You need to sync the midi or sequence in a note at the end of each part of the sequence that's in the same place. Then record the audio of each part to separate tracks in Sonar (without worrying about the sync). Once they're all in Sonar line up the note at the end (kinda like how film makers use the clapper board to sync up the sound and image) and you should all be in sync.

I  used to do a variation of this when I  used to record to a 4 track and copy the parts out to Sonar, we could only get them out one at a time so at the end of each take we'd glitch the recorder so it put a spike of noise across all the tracks, which we then used to align them in the DAW.

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