If you just want to use only the Triaxis do as Exo-metal said above.
If you want to switch between the Triaxis & Herbert you can use a loop switcher.
- Guitar to switcher
- Switcher send 1 to Herbert input
- Herbert send to switcher return 1
- Switcher send 2 to Triaxis input
- Triaxis send to Switcher return 2
- Switcher output to Herbert return
You can add as many additional preamps as the switcher can accommodate. I'm currently doing this with my bass setup. I use a Voodoo Labs Hex to run 5 preamps and Mesa Titan bass amp all through the Titan's power amp.