The BIAB Mixer on the main screen does not have Buss or aux outs but there is a feature that VST's can be inserted on a channel where two guitar tracks reside and fx's can be applied to both instruments.

Here's how I did it:

Example using guitars RT's 1572 and 1073

I used a midi style and replaced the #26 AC Guitar with RT 1572 located on the Guitar Channel

For plug ins I added PG 5 band Eq set for high pass filter; and PG Echo Chorus; Mixer Volume 88; Mixer Pan 0; Mixer Reverb 21 and tone 2

I opened the RealTrack Picker and Selected the Medley Button

The 1572 guitar occupied the first slot panned 64
I added 1073 guitar to the second slot panned -64

Selected Whole song and play simultaneously

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The result is the two guitars play simultaneously with the same effects applied across the track to both guitars.

The Plug Ins Tab accepts VST's as well as PG Effects.
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BIAB Ultra Pak+ 2021:RB 2021, Latest builds: Dell AIO; Windows-10-64 bit, AMD A9 Processor and 16 GB Ram Memory.