So I've put my project aside, but a few days ago, I had an idea that's as simple as effective.. Since I will primarily use my Arduino as an interface to Music Player Daemon
, I'll use socat
(netcat on steroids) as a bridge between /dev/ttyUSB0 and the (Unix or TCP) socket on which MPD listens. Use an interrupt to react on a button press and do a serial.println (send the command), use serialEvent to listen for the computer's reaction to the command I've sent and use the main loop to refresh my LCD screen a few times per second.
I think this is usable for connecting to any Linux service with a TCP or Unix socket interface..