I believe the DSP-4 retails for around $600.00.
Search on google and I think you might be able to get a better price.
The DSP-4 can do more things than most will ever need.
It has multiple parametric EQs that allow you to vary the frequency, Q, and gain. It can also be used as a crossover with anywhere from 6-24 db per octave slope.
It can be used with ANY amplifier with some adaptors and an external power supply. It plugs right into the QSC amps that have a DataPort input.
It does need to be interfaced with a computer for set-up. After you set the EQ, it is saved in the DSP-4. It is a fairly friendly program to use. It is very handy to use with a Real Time Analyzer program. That way you can easily SEE where your room peaks and valleys are and where to set the EQ. You can then see what it takes to get a flat responce.
Here is a link to the RTA software I have used the most.
http://www.trueaudio.com/rta_abt1.htmThe simplest version is a free download.