Why not just use VLC Remote instead.
Setup VLC Player from videolan dot org and assign the output to a DAW return in UC Surface software, this can be done on Mac or PC.
On the Studio 192 Sound Output (for Mac and PC) Maps to UC Surface like this:
Studio 192 - Output - DAW Return Mapping
|Studio 192 Outputs
||UC Surface DAW Returns|
|Main Out Left
||DAW Return 1|
|Main Out Right
||DAW Return 2|
||DAW Return 3|
||DAW Return 4|
||DAW Return 5|
||DAW Return 6|
||DAW Return 7|
||DAW Return 8|
Just assign VLC to play out of which set of outputs, link them to get stereo pan effect or do it manually.
Then get VLC Remote for your phone and remote control your MP3 player. You then have control of triggering your MP3 player remotely and the ability to control the level from VLC and/or UC Surface.