I was going to suggest cat5 cable. Multiplexer/demultiplexer and power source near the rockets.
That sounds like a nice system. 8 Wires make for 128 possible outputs.
I would possibly go for 4wires for 15 firing inputs (and an inactive code), A pair for return, and a pair for safety purpose. The firing system would ony be active if the pattern on this pair is the one intended (one high, one low for example. Needless to say, I would add ample capacitor delays on such a system, so that firing is not triggered when rockets are being installed.