YSF narrow, or YSF wide? If YSFN there's no need for the DV sticks, as YSFN is AMBE. If you're using YSFW, which is IMBE, then you'll want the sticks since software vocoders seem to have a tough time making the audio quality something you want to listen to.
Now, that being said...
There's a couple options here. Number one is you can try YSF <-> MMDVM_Bridge <-> MMDVM_Bridge <-> DMR. Connect one MB to the YSF reflector, and one to Brandmeister. Also, make sure the ports on the two MB instances are set to send/receive to each other. I think you may need YSFGateway between MB and the YSF reflector, but it's been a while since I've set it up... Number two is YSF2DMR, but that's outside the scope of DVSwitch. Both of these options will work for YSF narrow.
If you're using YSF wide, you'll need to put Analog_Bridge in the middle, so that the data to/from DMR gets transcoded from IMBE to AMBE and vice versa. That's where you'll need the DV sticks.
The looping thing, it might be caused by someone with two personal hotspots running on the same frequency in close proximity to each other. This is a common occurrence on Brandmeister, where someone has a hotspot in their car and one at home, and you get looping audio when that person's car pulls back into their driveway. Checking the ID that's transmitting when you experience the looping audio may give a clue as to the offending hotspot.