Panning and Buses

The best way is to put your amp sim on each of the guitar tracks feeding the bus.
 
A soon as you put it on the bus you'll lose the unique panning of each track

I just did it and made it work. I used the "send" of each guitar track with "post" disabled so the signal will be sent even with the original guitar tracks faders all the way down (I'm assuming you want 0% dry guitar signal and 100% affected by guitar processor in bus). I panned the sends hard left and hard right, not panning the tracks themselves. I inserted TH3 and the two guitar tracks were panned hard left and right with the TH3 processing them both.
 I'm not sure how you will get the hard panned guitars in the bus back to a point where they can be mixed and panned to where you actually want them (assuming you don't want them hard left and hard right in the final mix). I tried using patch points but even when I assigned the output of the th3 bus to a patchpoint, then created two new tracks using the mono left patchpoint as input for guitar one and the mono right patchpoint for guitar two, those tracks still wound up having one guitar left and one right. I rarely use patchpoints and I don't understand this behaviour. Maybe someone will have some insight on that.

It can depend a lot on the plug-ins (including the amp sim) too. Plug-in inputs may be summed, treated as stereo (which is probably not what you want) or as two separate channels (which is probably what you want).
 
Instead of routing both guitars into the same FX chain (something you probably would never try with a real amp and effects) put FX chain in each track as mentioned above then freeze or bounce and archive the tracks.
 
In general stereo tracks/buses should not be used where the two channels need to be completely separated.

Ive experimented with this over the years and have found what im sure you already know now.
Putting the guitar sim in each separate track as Jonsey mentioned is the best rock to throw here.
Put 1 sim in each track then pan them hard left and hard right / send them both to your guitar Bus.
 
I typically send all distorted guitars to one Bus and all semi clean to another bus.
You can get away with EQ the buses to get a independent sound (I use Softube's Grand Summit EQ/Compressor)
But even then I find its not as powerful as if I put it in each track separately.
 
Only using delay, Reverbs, Chorus FX for buses to be feed by a send or sometimes using it on an instrument Bus to feed a small group of tracks.
 
there are no rules of course but I wouldn't be worried about saving resources (if that's why you are trying to share a sim by using it on a bus) Most Sims are not to CPU heavy).
 

Kev999
Neither. It's due to the fact that the amp sim is a mono effect.

Amp sims are not mono effects.

TH3 is definitely a stereo guitar amp sim. Maybe it is the only one. I ran a bass track and a guitar track into a single instance of TH3 one left one right, and they came out still panned left and right and effected.
 They may not be stereo in the sense that if you input a mono signal it may not be "stereo-ized" but if you input a stereo signal the two channels will be processed independently and they will retain their panoramic placement.
 
From page 24 of the TH3 manual:
WIDTH: sets the stereo width of the input channel. 0 equals to Mono, 100 to stereo and -100 to inverse stereo (swap of L and R inputs) PAN: sets the panpot or panorama position of the input channel at the output. For stereo signal it acts as a balance control: at minimum it will only pickup the left channel signal, at maximum only the right channel will be preset at the mixer output. LEVEL: the reference level of the channel. BALANCE: this control allows you to dial-in a real-time balance between the two mixer channels. MONO/STEREO: sets the output mode of the mixer. Mono merges all inputs to mono.
http://www.overloud.com/d...3-user-manual_5841.pdf