It sounds like you're used to the amount of treble energy in whatever cans you're using (which happen to be...? UERM customs?). I would try adding a high shelf filter, say +3.5dB at 2500Hz, bandwidth 2 to bring the treble energy back up. Basically the idea would be to have the curve stick to 0dB on average while evening out the spikes and dips in response.
Also have you played with the bandwidth setting on your filters, how are you arriving at your current settings?
Finally, the UERM are deep insertion customs right? I wonder, with the depth of insertion of those things, perhaps the only real resonance you'd get is the one above 10kHz. Then too, these being customs, I wonder if they'd have measured the distance to your eardrum while making the mold and taken that into account too with a custom filter in hardware (doubtful, but I'd think it could be done) You might be the first guy to join this thread using customs, maybe you should shoot UE an email about this "resonance" thing and see what they say about it.