If you are looking at increasing the number of simultaneous tracks, you could use this, however there is a bit of work to get everything fully into the PC.
As I couldn't find any detailed info on your recorder this is all speculation... You might be able to use MIDI to 'sync' the computer and the Yamaha. What you can do then is record to both the PC and the Yamaha at the same time (so assuming you have a stereo card on your PC a total of 6 individual tracks), then later you would have to transfer them onto the PC via rca cables or the like so each track was individual. Mind you, in doing this you would be adding another D/A -> A/D conversion of it which would reduce the quality of the audio.
Other option is if there are 4 inputs on this, you should be able to use it as a mixer and record 2 tracks down to the computer.
I'm assuming posting in this forum you have Cakewalk software and are looking at integrating both?
Daniel