40hz room mode RPG Modex Corner trap?

I understand that the PARC might be a bit expensive. However, the Behringer DEQ2496 would do the job for you. See the several threads about this remarkable unit. By the way, Rives audio will tell you that LF room resonances, like 40 Hz, can't really be controlled by room treatments, and that is why they came up with the PARC.

Jburidan...The PARC is by all accounts a fine piece of equipment, and if you can afford it and buy it I am sure you will see a big improvement in your system.

However, for other readers, if not you, I do want to correct several comments and misconceptions about the Behringer.
1..Unlike the PARC it can boost as well as cut. (Word on the street is that a future version of PARC will do this also).
2..It includes a 61 band specteum analyser (or Real Time Analyser, RTA) so you can easily see what is wrong and how it gets fixed.
3...It has a completely automatic equalization process that eliminates a lot of guesswork. (And is fun to watch).
4...As you say, it has many (31) bands, with bandwidths adjustable from 1/3 octave and up. But it also has several bands of parametric equalization, and several notch filters (cut only like PARC) with bandwidth as small (sharp) as 1/60 octave. There are a bunch more things it can do, but with the possible exception of delay (to compensate for speaker locations) you probably would not use them in the home audio application.
5...It is digital. IMHO, to reject it simply for this reason, without ever actually listening to it is stupid. The A/D and D/A are modern 24 bit modules run at 96KHz. FWIW, 24 bits gives resolution 256 times better than a CD, and the bandwidth is more than double. The actual digital processing is done by a 32 bit Floating Point processor, so there is no issue of resolution for this function. Of course these are all words, and one should not accept them as a garantee of good sound any more than one should accept your suggestion that the sound must be bad. Please reserve judgement on how the Behringer sounds until you hear one.
6...Finally, it costs about 1/10 of a PARC. This is a good deal for a spectrum analyer (to help with your PARC setup) even if you are never curious enough to put the Behringer in your signal path.

Nikturner920...To my ears, with Channel Islands D-200 amps driving Magneplanar MG1.6 through 4 foot Goertz cables...YES.

However, if you determine audio quality by how much it costs, check out the Reference Audio Mods changes, available for the DEQ2496 and costing about $1500, including $600 output transformers said to reach the audiophile heights.

Again I repeat my mantra...Buy it for the RTA. The EQ will sell itself if you try it.

Nikturner920...Although I do have LP, my best source (IMHO) is a Denon 2900 with Underwood mod, via unprocessed pass through of Rotel 1066.

My three DEQ2496s are between the preamp and the power amps. It would be better to use a TAPE loop (unaffected by volume control) but that is not available for multichannel. I could put the DEQ2496s between the Denon and the Rotel, but then I could only use them for disc player programs.

For 2-channel you could run digital from a cheap player into the Behringer, which would be an equalizer and DAC rolled into one, and then out through a passive attenuator to the power amp. Lots of Bang for the Buck.