At first I thought that they would not be able to sync because nl2.x is a gba game and lsdj is an old game, but that was not the case.
Also I found that using a DMG/CGB cable you can sync 3 gameboys at once!
The yellow cgb is running lsdj and is the master, it is set to 'nano' sync. The blue sp is running nanoloop 2.3 demo, and the DMG is running lsdj, set to midi sync, but I think setting it to slave works too.
To make nl2 receive sync messages you select the 2 triangles that look like a fast forward symbol and press a+b. If you stop the master, nanoloop will sort of pause where it was up to in the sequence. To set it back to the first step again and make it wait, just select the 2 triangles thing again and press start, then a+b again.
I used this cable: http://www.nonelectronics.com/catalog/i … ucts_id=10
Kitsh's cable should work too: http://kitsch.bigcartel.com/product/dmc … link-cable