(See PG 17 of owners manual)
Why are there 24 sub-master output jacks on an 8-submaster mixer? This is called "triple-bus-sing." Triple busing is a way to rout your sub groups outputs to all 24 Sub-master/Tape outputs when supplying signal to three 8-track recorders. The signals you send to the sub outputs will appear on 1-8, 9-16 and again on 17-24. You simply put the tracks you want to record in RECORD mode, and the other tracks (not in record mode) ignore the signal. The sub-master outputs provide more than enough signal strength to do this.
That way, you can feed a 24-track deck (8 tracks at a time) without having to constantly re-patch. Connect the Sub-master/Tape Outputs to the corresponding inputs on your multi-track, using only Sub-masters 1 through 8 for one 8-track deck, tracks 9-16 for second deck and 17-24 for third deck. Pretty cool, huh? You just arm up to eight tracks at once.
See chart below showing bus routing:
Triple-Busing Chart:
Console Bus 1: Sub-master 1, 9 and 17
Console Bus 2: Sub-master 2, 10 and 18
Console Bus 3: Sub-master 3, 11 and 19
Console Bus 4: Sub-master 4, 12 and 20
Console Bus 5: Sub-master 5, 13 and 21
Console Bus 6: Sub-master 6, 14 and 22
Console Bus 7: Sub-master 7, 15 and 23
Console Bus 8: Sub-master 8, 16 and 24