Louis, a couple of thoughts:
For reasons of economics, you should try the 2-driver setup; as you already have a suitable cabinet, this would be the easiest and most cost effective way to start. At 94dB, and wired in parallel at 4 ohms, it should work very well with the Zen. Also, as an option, if the drivers were wired in series, it would be 16ohm, and many amplifiers, particularly SET amps, benefit from higher impedance.
But a 4-driver array could be a superb choice. Needing a larger cabinet, it would be a nice little floorstander, eliminating the need for extra-cost stands. It would bring sensitivity up to about 97dB, and would have two viable wiring options: all parallel at 2 ohms for the Zen crowd, and combination parallel/series at 8 ohms for most everyone else. This would be a killer combo for other low-powered triode amps, like the Bottlehead Paramours, the Fi X, Jeff Koernoff's 45 amps, etc.