YouTube – Atari 2600 Full MIDI Interface for Music. just the proof – no real info about it, but this is what littlescale says:
I love the sounds of the Atari 2600. I made a MIDI interface that gives you full control over the sound output of an Atari 2600. You can watch a quick demo here.
I really want to thank Paul Slocum and all of the fantastic work that he has done for the inspiration.
or just this: SIO2PC. (thx summa @ Forum for info): Atari 2600 an MIDI