Anyone using beatbuddy through Boss Gt-100?

I’m looking at running beatbuddy through gt100 and Marshall tube head. Does this path work well?

It wouldn’t be my first recommendation. Both the BB and your GT100 would prefer a Flat Response, Full Range amp, like a keyboard or a PA, But, if the Marshall is all you got, you have to make due. The recommended cabling path would be:

guitar>gt100>BB in> Marshall effects return on the back side of the amp.

This bypasses the preamp section of the Marshall and goes straight to power amp. Depending upon the model, there is usually a volume control for the effects return, which would then adjust the volume of your overall mix. You don’t want to color the drums with distortion, delay, etc, so you want those after your GT 100.

The issue then becomes the speaker you have selected to use. Your typical Celestion guitar speakers (Greenbacks, Bluebacks) are not Full Range speakers. An exception to that is the Seventy80 which is often found in modeling combo amps.