well, according to the specs of the HD24 it does send out MTC....so you should be able to just go MIDI out of the ADAT into the MBox2.
In PT go to Setups-->Peripherals-->Sync and check to make sure Device is set to Generic MTC Reader and port is set to either Any or your Mbox2's MIDI I/O.
Configure the HD24 to transmit MTC at the proper frame rate (via its MIDI pages), and you will be all set. Tell the HD24 to generate MTC.
Put Pro Tools online (Ctrl+J)
When you press play on the HD24 it should then send MTC out to PT and sync the two together. You should also be able to setup Pro Tools for MMC and just connect MIDI out of the MBox2 to MIDI in of the ADAT...if you wanted to control the ADAT that way.
Unfortunately, you probably won't be able to get clocking information from ADAT to PT because of the lack of ADAT Optical on the Mbox2 and lack of S/PDIF on the ADAT.