There is plugs that can do the conversion for you... The conversion doesn't matter, it's just a plug, a way of connecting. The plug is actually a female plug on one side and a male plug of a different type on the other side. Inside there's just connections... Nothing more.
Now you gotta be carefull with TRS plugs. They are used for some different things.
- The first on is stereo, tip is your left signal, ring is right (or other way around) and the sleeve is ground.
- Second is balanced. Tip is hot, ring is cold, sleeve is ground. If you don't know what balanced is, look it up. This is important to know.
- And the third use is with inserts on a mixer. Here the tip is send and the ring is the return of the signal, or the other way around. Depending on the manufacturer. Check the manual of the mixer in question for this....
My guess is the Motu uses TRS jacks for balanced signals, so I wouldn't put in a stereo signal. You can put it in, but the 2 signals just get subtracted and end up as a mono signal...