Hi @marccobe,
oh, that would be great if the Trellis could be connected via USB and exchange OSC directly like a standard USB midi device. I am afraid it is not that easy (at least not to my knowledge). There is a thread at Lines, where I did ask for help to get me going with my Adafruit Unztrument (which is based on Trellis key pads).
I have it running with a serialoscd implementation by Szymon Kaliski. This works based on nodejs, so I would have to use Javascript to link the Unztrument to Sonic Pi.
I am still looking for a solution to use the ‘standard’ serialoscd and use the Unztrument like a monome clone. But this seems to require to flash the Arduino’s FTDI chip (see a blog entry of Szymon, where he explains why he reimplemented serialoscd: “… either flash my Arduino FTDI eeprom …”).
I did try to flash my FTDI chip but did not suceed yet. So right now I am also stuck with my Unztrument, because it does not communicate like any other standard USB midi device.