This is a live Chiptune set recorded from the This Week in Chiptune show hosted by Dj CUTMAN.
Trey Frey uses 4 gameboys running a software called LSDJ, and it make music with 2 gameboys at the time. With the mixer he chooses between the two pairs of gameboys playing to change songs. It is very rare, because most of the Chiptune musicians only uses one gameboy per song, but there are a few weird dudes like Trey Frey and Pain Perdu who uses two or three gameboys to make only one song.
If you liked this go listen to Refresh in his Bandcamp.