What UI?
The basic players just use buttons for actions, but don't have a display. I don't know *anything* about Rasp Pi, but I read that Adafruit Arduino shield walkthrough and it seems very straightforward. There are pads for buttons and function calls for them, so you just need to copy and paste the same code as appropriate.
In theory. I am way too out of the loop on this stuff to be of any use, but it seems pretty straightforward... and from what little looking I've done over the past few weeks, I think there are plenty of resources where you can get help. I'm hoping so, anyway - I'm going to need it! Really, though, Arduino is aimed at beginners learning about electronics and coding - it just can't be that hard to do basic stuff out of a kit.