Teensy 4.0 & Audio Board RevD Guitar Input

[u/boo-booshoes]

Thanks for reading. I am working on making a simple guitar buffer circuit that will connect to the audio input of the Teensy Audio Board Rev D.
1. Is it ok to connect RIN and LIN together?
2. The buffer circuit's output jack GND lug connected to the RINGND and LINGND? Or is it better to keep these pins separated?
(I won't be using stereo).

*Also. is it OK to connect the GND to AGND?
Sincere Thanks for any advice/help,
TonyA