My question is: does anyone have a "best" way to connect and use an RP1000 with an RP355? I will have the end result of the RP's going back into my Roland GR-33.

I decided to route the RP355 as a stompbox by using the mono stompbox effects loop. I am a bit disappointed that there isn’t a stereo effects loop on the RP1000. 

I also have a dbx goRack and the Behringer UMC202HD. Prior to buying the RP1000 I would route from the GR-33 guitar out into the input of the RP355 and the stereo outs of the RP355 back into the GR-33 stereo returns. The GR-33 stereo outs into the dbx goRack stereo inputs via XLR plugs and stereo outs into the UMC202HD. The UMC202HD stereo outs into the Behringer K3000FX Keyboard Amp.

Guitar -> GR-33 Guitar Out -> RP1000 input -> RP1000 StompBox Loop Send -> RP355 input -> RP355 Output -> RP1000 StompBox Loop Return -> RP1000 Left and Right Outputs -> GR-33 Left and Right Returns -> GR-33 Left and Right Mix Outs -> dbx goRack stereo inputs via XLR plugs and dbx goRack stereo outs -> UMC202HD stereo outs -> Behringer K3000FX Keyboard Amp.

Anyone have some thoughts or experience on this?
Thanks in advance,