if I were you I'd keep using the 909 as a master tempo. solid and reliable as ****.
but otherwise, why not use ableton as your master?

the 909 has 3 tempo modes, 1 to use it as a master and 2 as a slave.
of the 2 slave ones, one will hold your 909 faithfully to the master tempo, the other will mean it simply triggers at the same time as the midi master.

if I remember rightly, hold shift and tap the "tempo mode" button until a "0" is displayed in the far right of the bpm display.

like I said, if I were you, I'd keep using it as a master. it's far more reliable than any computer I've ever used.