I understood the advantages of choosing those slopes to be less interference between the drivers across a given 3d space. That seems attractive; however, I'd have to move the xover up higher.

Can you give advice on how much of a difference this makes in sound quality and whether you think it would be worth the trade off in potential MR behaviour? See addtl. data below.

I have listened to the Radian driver and DDS waveguide and it sounds good w/ the LR 4th order at 800hz. I will not go lower though. With the D131, the JBL folks claim it goes up to 5K; however, I've not measured it yet (I'm helping someone out of my area). Given its a 12" w/ large aluminum dustcap, I'm expecting some nasty break up modes on the way to 5K. Certainly when I've listened to the system as is, the MR clarity is rather poor.