... ... I can't find input specs online. So, safe bet is to set the Sans Amp to a tone you like with no obvious distortion, and play the bass > SA > R100. Set the R100 master volume to about where you have to talk loud to be heard over it, with no overdrive, but everything else where you like it. Start with the SA output low and slowly raise it. ... ... ... Remember that the gain knob works like an input pad on a mixer; it's not a traditional amp gain circuit. ... ... ... Also, you could just go into the effects return.
From the online manual:

