This is not an advertisement, it's just the tool I know of.
I want to explain how you can use other JACK tools in your setup and.
Open the program and go to settings (hamburger menu in the upper left corner). Go to "Audio" and choose "JACK" under "Technology".
Turn the guitar/bass volume in Rocksmith down. Open Tonelib-GFX. You should now hear your audio being processed by Tonelib-GFX instead.
This has significant delay, so you might not want to use it. But go ahaed and try.
I had more luck starting Tonelib-GFX first, then Rocksmith.
Patchbay:
You want the output of Tonelib-GFX as the input for Rocksmith. The output of Rocksmith is the only one going to your audio output device.
The best way to reroute this is to change one line, then window-focus Rocksmith. Change another one, window focus Rocksmith. Repeat. Be patient.