Its not either or, use midi mode only as slave mode will start your project a few ticks behind due to the difference in sync methods of midi vs lsdj.

This took me a few minutes as well when I started using Ableton. Just go through all the settings and make sure it's sending a master clock signal.

Of you put it in midi or slave mode and press start on the gameboy, it will say WAIT and should start playing when it receives a start signal via midi...

Put LSDJ in slave sync mode.
Arduinoboy - LSDJ midi slave sync.
Press start in LSDJ (it's now waiting for midi signals).
Start your software sequencer (sends start command and midi clock).
Should play in sync now.

I was wondering if anyone could help me out. I'm trying to get Ableton/Reaper to send midi to my Arduinoboy and get LSDJ to start on command. I can't seem to figure it out, i've tried every mode on my arduinoboy and so far no luck. What mode should my arduinoboy and LSDJ be in? Also what midi channel should I send on and what midi notes do I need to send to start and stop LSDJ? I'm essentially trying to get my Game Boy to play along with tracks in ableton and reaper.

Thanks!