I think the main advantage of the rd series is the low xover point. It is like having a full range driver. You could use a first order xover. I heard a pair and they are very good. One issue is the low effency.

If you realy like the low xover feature these will be a good choice. You may want to listen to ribbon drivers also before deciding. The xover point will be in th 2k range though.

My array gets very quiet when listening closer than 2 ft.

-Linc