Well I've never tried this, but I should imagine it would be something like:
Multi-Track Recorder>Multi-Channel Mixer>Multi-Input Audio Card>Sonar
On the other hand if it's a two-track recorder:
Recorder>Audio Card>Sonar may work.
But there probably wouldn't be much point if there are already multi instruments recorded and mixed onto the tape. You can't re-mix from a two-track tape unless there are only two instruments and they are recorded on separate tracks.
But you could do some overdubbing, however you may be plagued by tape hiss from the original recording.
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BluesMeister