I agree with petes assesment, 4 would be bad, just build a new box out of 25mm MDF (heavy but rigid) and put the driver on the front, and one PR on each side, then make certain you keep the box 4 inches or so away from any wall. This design should be much more stable, as well as less resonant. Put the driver and PRs in the center of each side and brace above and below them that should stop almost any resonance. Stuff the box lightly and youre laughing. The best part of this design is that you can do it for only the cost of a sheet of MDF.
