Peak limiters are usually not useless so long as your amps are relatively matched to the program power of the speakers. Limiting on most processors is, in fact, still peak limiting. You only find rms limiting on select top end processors and the majority of those are ones that are built into amps like the I-Techs.
Now the cases where peak limiting may not be all that helpful is if 1) your power amps are too big for the speakers, 2) you overdrive the shit out of your signal chain or processor, 3) the limiters are of shitty quality and can be "punched through" easily, 4) sine wave heavy trance type music where you're pushing your system to the edge (in that case having your amps sized smaller than program power rating & closer to the rms rating would be a good idea). I find with cheaper DSPs, the limiters often not only don't sound very good when you're hitting them, they also may not limit all that well either. FWIW, peak limiting has been doing a decent job of protecting systems for a long time. Of course, these are systems with well matched amp, speakers, and processing. The article Bennett wrote talks about using much bigger power amps than the speakers are rated for, and that can work very well with properly calibrated rms limiting. And you likely to get a noticeable bump in average output and headroom by doing so. But for the time being, that takes some big wallet amps and processing.
As for how well the limiters in your DCX work in terms of punch-though and sound quality, I haven't used one. But I suspect other here have and will chime in.