Is this a difficult thing to comment on?

Not difficult to comment on.

You ask ... common ?

:? ... not for me as i tend to just record the multiple guitars to individual tracks.
Today DAWs have track count for days and even on LE I used to use multiple sessions to get the track count.
Now we can juggle the available voices ...
I have HD for mix down.

In the past when I have done multiple sources to a single track I used an analog mixer to do the summing.

Technically it is very do-able so I don't see a problem.

Thats good to hear. So technically theres nothing wrong with it. Pretty much like summing it before entering the box to an audio track but this way im summing internally to the track.

without getting into the pedantic and the never-ending analog / digital argument and then, the PT factor.

nothing wrong with the idea

what do you need 3 aux's for? why not mix 3 mics into ONE aux if your just trying to blend before comitting to hard drive? don't really understand the point of it.

you would have much more options at mix time if you record 3 tracks and then submix guitars to an aux in protools or whatever you use. or if you dead set on mixing analog, send 3 outs to a board and record the line in, and submix outside. but all of this *should* be reserved for mix time, cause you can't undo it when you do it on the way in.

its amazing how much changes in a week or two when you hear it with different ears.

steve