Personally, I wouldn’t recommend recording an arranger that’s using audio content internally. A nice Zoom type pocket recorder (4+ channels if you’re adding other gear) gets the job done quite cheaply, and doesn’t tax the arranger’s CPU and HD any more.

A whole boatload of Real audio tracks is going to keep the HD busy. Add that to the encoding and live storage of a mix file, this may tax the system too much. This is why I always keep my little H4n pocket recorder handy…