Hey Bo,
I also prefer a "flat" sound. For me, the accurate reproduction of sound is most important. I don't like any passband overemphasized.
Good points on phase. I hadn't considered running my subs 180 degrees out of phase.
It might be a while before you hear from me a again. I'll be busy positioning speakers, cutting cables and taking measurements. But, I will be back to post results. Thank you for your help and guidance!
I also captured some high-resolution RTA readings. There were some questions around slope. For completion, here are the new readings. The higher resolution exposes more ringing, but at least the slopes look steeper...
10Hz - 80Hz:
80Hz - 800Hz:
800Hz - 8kHz:
8kHz+:
-Brian