Crap. I just had a huge response and lost it.
Long story short...
I was thinking about the crossover.
But if you're using the receiver for your system XO, you can use the DCX XO as a LPF with more slope options than the EQ filters.
Am I right that the LP EQ filter is tapering off >45Hz, causing the rise in natural response to end up more flat?
The XO in the DCX is basically a highly adjustable band-pass filter. The upper and lower ends can be adjusted to any frequency, with any available slope.
Setting it so the bottom end had nothing (flat) and the upper end to 45Hz, 12dB/octave would be the same as applying your current 45Hz LPF, except it's on the output instead of the input and has more adjustment options. Then you can try changing the frequency point and/or slope to fine tune that upper end (if it even will flatten any more).