Reaper is good, too, but not free after the first month. You may be able to designate two stereo channels on the R44, I do not know, and then you will be mixing two stereo channels. This means they will already be panned to stereo. Either way, Audacity or Reaper would work. I use SAM. There is an LE version for ~USD50 which is a good buy. If you want to stay as economical as possible use Audacity. It has a ton of plugins and lots of folks use it so there is a lot of help out there, too.
Cheers