Reamping with UR-RT4 and Reaper

Reamp - URRT4 - Reaper - Hi. How can I playback and simultaneously record? Thanks! Can send 1) MONO OUT Ch 1 - to Boss Pedal (lower Output vol in Daw) to Amp or 2) MONO OUT Ch 1 - to X-Amp to Amp. Problem happens when I try to record a micd amp - no matter what channel the mic is on 1-4 input on the URRT4, the mic sound bleeds into the MONO OUT creating a feedback loop. Stopping playback of the dry guitar to test the SM57 mic, the mic works fine.

Got it to work!!
Reaper DAW
Trk 1 = Dry guitar source
Add New Hardware Output - UR-RT4 MIX 1L = Trk 1 Mono Out (Rear)
Mono Out - Reamp box - Amp

Trk 2 = Rec Trk
SM57 Mic Trk 2
Arm trk 2 input 2
UR-RT4 DSP App- MIX1- all knobs bright
CH 2 Headphone out Lit = headphone out to Mono speaker
Feedback Loop Broken!!
DSP App - When trk 2 is muted - Can record amp

YouTube - Reamp Dry Guitar Track with Reaper - Simple Way

YouTube - Reamp Dry Guitar Track with Reaper - REAINSERT