I am not aware of anyone who actually has the IPR3000 in stock, or has been able to get one. These amplifiers have been delayed well over a year. Peavey says the problem is parts availability.
The reviews I've read of the IPR1600 are basically what you'd expect, good amp for the price, very light-weight, but don't plan on running it into 2 ohms per channel because it will overheat if driven hard. Still, a great value for the right setup.
The DSP is significantly less powerful than on the Crown XTi amplifiers, the only real direct competitor to the IPR DSP. It's a whole lot better than the analog crossover features built into many inexpensive amplifiers. EDIT: It is much better than the simple one in the Behringer EPX3000. END EDIT.
When the higher-powered versions of the IPR amplifiers eventually ship, the 4500 and 6000, they will not be capable of 2 ohms per channel, or 4 ohms bridge, operation. This is a design limitation that is well-understood by Peavey, and is the reason they have not included a bridge mode on the lower-powered models (to keep that feature, or lack of, consistent across the product line.)
EDIT: The Behringer EPX3000 is another good amplifier for the money. Again, the built-in crossover is largely useless; but in its job of, well, driving speakers, it works well and offers a lot of power for the money. I own two of them and am likely to buy one or two more in the next few months as I replace a heavy RMX2450 and upgrade my B-rig subwoofers. If I was unhappy with the ones I own, I wouldn't be buying more!