Create a stereo AUX track.
Set its input to any available stereo bus.
Set the output of all tracks(except the guitar) to feed that stereo bus.
That will make all the other instruments pass thru this new AUX so you can use it as a master fader to down down everything except the guitar.
Now that you know how to create a "submaster" bus, you might look at why you need it(sure, there are many good reasons to use it, but "damage control" is not usually one of them). How high do the meters go on all your sample tracks? If they are all near the top, open those instrument plugins and lower the output by 8-10db. Back in the analog days, we always worked to keep signal levels hot so that tape noise would not be a factor. With digital recording, there is no noise to overcome, so recording and track levels don't need to be any hotter than tickling the yellow on the track meters. Its a common newbie mistake to have tracks that are as hot as possible and then the track fader is sitting at -20 or -30 in a mix
