RB merges everything to a temporary stereo wave file first, then asks what format you want to convert it to.
What I don't like is (at least here) if the wav file didn't already exist, RB leaves a blank empty wav file on the drive after doing the conversion.
It doesn't do this when using the Convert to WMA routine in the same drop down.

I do not work here, but the benefits are still awesome
Make your sound your own!