If your going to setup like the top picture in a long and skinny bar to carry the sound then delay the speakers as shown in the diagram about 1ms per foot away from the first set. You use the delay to prevent echo's and reverb, not comb filtering.
The second picture is if you have the 4 speakers all facing into the dancefloor, then no delay is needed.
If your using subs and tops you need a crossover anyways. A limiter included in the dsp will also protect your speakers from DJ's abusing and possibly damaging them.
The dbx driverack pa + has an auto EQ fuction to help EQ your room. Works well on the mids and highs. The lows still need fine tuning by hand. Its a good unit but pricey.
The dcx2496 has parametic eq's, but no auto-eq function so you have to tune your system yourself. Its a good unit as well.
At our venue we use a dbx260 and the behringer dcx2496. We have 4 speakers into the dance floor like the second picture with no delay. Further back (65 feet from the mains) we have speakers for fill like in the 1st picture with delay added. It sounds like a DJ not beatmatching on the mix without the delay.