Good chance they must not sell them, then.
Stores have an understandable habit of warning people off of stuff they don't sell. I'd be really leery of anyone who claims that parametric EQ shouldn't be applied to subwoofers. On the other hand, a lot of people don't think EQ should be applied to the rest of the signal. At any rate, you'd only actually apply the EQ to the low pass feeding the sub (ie everything lower than 80hz or whatever x-over point you're using).
I use a Behringer Feedback Destroyer, model # DSP-1124P. It can be found at a variety of online dealers; seems like I bought mine from
Lentine's Music , but I've had it for quite awhile. It has a lot of pro audio functions, but all you'll want to use is the parametric EQ features. One downside- this unit is a bit complex to set up until you get the hang of it, and the manual is not helpful. There're a couple of really good online tutorials posted by 3rd parties that will save you a lot of grief. Also, it has only TRS (tip ring sleeve) and XLR inputs/outputs, so you'll either need cables with an RCA plug on one end and TRS or XLR on the other or an adapter. Both are fairly cheap- you can get an adapter
here.
The next model down in Behringers' line is simpler to configure ( the ULTRA-Q® PRO PEQ2200) but not as flexible. It only has 5 bands and no electronic memory, but it will do. You're unlikely to need more than 5 bands to EQ your sub, anyway. Each channel will interact somewhat with the others, and it would take a novice forever to try to wrangle more than that. Be sure to use it only to cut, not to boost.
There's a lot of sophisticated test gear available, but you can do a pretty good job with a Rat Shack SPL meter and a disc of test tones. I like the Rives CD as it has tones calibrated for the known deviations from flat of the Rat Shack meter.
