I had originally intended for us to use only the leftover MLB players in our AAA, but some teams had tons of real MLB players available to draft for AAA while others had very few...I believe that this would give even more advantage to those teams with tons of MLB AAA over the ones with little to none to use.
The random AAA is really a crapshoot, so having sure thing MLB AAA is probably still more advantageous.
That being said, all AAA are available to use. I prefer as many real MLB players as possible, if we at least rename our AAA after real life AAA, we can still upheld the "spirit" of the league.