I've been testing my JergulorX pads the past few days, fiddlin' and tweakin', and discovered that the back vents with the Creatology foam were produce a serious bass response to the point that it was rather "bloomy". For some songs that already have a serious low end, that tended to intrude into neighboring frequencies, making certain mid frequencies recessed, esp. rhythm guitar, etc. Mids like vocals and such were fine. While the thumping, rumbling bass was fun at times, the overall sound was less than accurate.
I did a quick test by covering the open back sections with electrical tape, which definitely reduced the bloom. In the end I redid the mounting rings with just the double-sided, hole-punched photo stickies (I doubled them), and now the sound is much more accurate, but those songs that have some serious low end are still quite satisfying.
My chain is:
24/96 FLACs -> foobar2000 with Output set to U2 USB DAC in WASAPI Event Mode -> USB extension cable -> HiFimeDIY USB isolator into U2 Sabre DAC -> AudioQuest Golden Gate mini-to-RCA -> Schiit Lyr running Super Cryo Reflector 6N23P-EV Military Matched Pair -> plusSounds custom cable -> HE-500.
I've also got custom grills like jerg's, with a sheer organza fabric dust shield (quite see-through). Oh, and I did the felt mod taped to the metal frame behind the grills.
Not sure if that's of any interest, but figured I'd share it.
For now, I'm a happy camper
Did you do the outer ports step on the pleather pads?