I don't mean to step in on Gary's thread, but I got Guitar Rig 5 late last week and I haven't slept since! :)
I too wanted to record the exact audio result of a performance given. One thing I noticed right away is that many of the modulation effects in GR that involve LFOs or the like don't re-sync to where they were when you recorded. Thus, the super-cool whammy drop that (when recorded) matched perfectly with the flanger sweep (blah blah blah) plays back differently each time. The re-syncing might be a preference however, but even if that were the case, it would mean you would have to start from the beginning of the project to ensure the sync unless you had it syncing to every bar. Eddie didn't sync to squat in '78, right? Why should you?
ANYWAY - to answer your question:
1) Make an audio track. Insert Guitar Rig.
2) Change the OUTPUT of that track to a bus. Let's just say Bus 10 for now.
3) Make another audio track. Change the INPUT of that track to BUS 10.
4) Record enable both tracks. Bring down the fader of the second track to avoid the 6dB boost you'll get by double monitoring both sources.
5) Go into record mode - Play like the guitar god you wish to emulate.
6) You will have recorded on both channels. The first track will have the straight, unaffected sound, but the second track will have recorded the audio output of Guitar Rig. You can delete the first channel's audio if you want.
Attached is an image of the two channels to help you. As you will see, I used Bus 20.
In my rush to make the screen shot, I didn't make the second track a stereo track which it should be assuming you selected a stereo instance of Guitar Rig in the first place.
Hope this helps!
[url=http://www.macprovideo.com/forum/upload/upload/server/php/savedfiles/files/mpv_42132_114133_Guitar_rig_record.png] [img]http://www.macprovideo.com/forum/upload/upload/server/php/savedfiles/thumbnails/mpv_42132_114133_Guitar_rig_record.png[/img] [/url]