Something isn't right here...What HU are you using?
I have been running mine for over a month with 150wrms strapped on them and these are my honest findings:
On my 880PRS with the BBE and Comp/BMX off and running flat except for a 3dB boost @ 31.5hz, 1 dB boost at 50 hz, and a -3dB cut at 3.15kz, I was running these crossed at 63hz @ 12dB/octave and they were as clean as can be, my pant leg vibrating making me think my phone was ringing. I can turn them up louder than I can stand to listen to them and still they are as clean as can be.
Now that I have incorporated the BBE feature into the mix, which has helped bring the guitar passages out of the murk a little bit, and I have it set at the 0 level, and have needed to cross the OEMs now at either 80hz @ 12db/oct OR 100 or 125hz @ 6 dB/oct. The 80 hz setting is fine for about 99% of what I listen to at that setting, but every now and again I will come across a really hard hitting song in that 80hz region that wants to bottom them out.
The BBE feature obviously is incorporating some kind of boost to the lower frequencies which is causing this to happen. But again, this is EQ specific. I am running them this way because it sounds better to me with BBE on and my mids crossed higher than with BBE off and mids crossed lower. With a truly flat, or close to flat EQ, in a fully deadened and sealed door, and a solid mounting baffle, these things should have no trouble accurately reproducing even the lowest of midbass frequencies with 150wrms on them. Start throwing in all the "gadgets" on these HUs and things can change in a hurry, which is not the speakers' fault.
You sound like someone who knows well what they are doing, but if you are anything like me, sometimes something can slip thru the cracks and leave you dumbfounded even if it is simple...double check the settings and gains, etc.. Almost sounds to me like an EQ feature is turned on that shouldn't be, or you dont have enough power for them and might be clipping the amp to get them loud enough.