There are better choices than the large RD series drivers. One problem is the really low sensitivity. Power handling limits the overall output as well. The use of Multiple Neo 8's are a much better choice. The moving mass is much lighter and control is much better as well. The smaller Neo's also sound much better than any other alternatives. Plus they can be crossed fairly low in the 800 to 1000Hz range and distortion is still kept really low.

The pdr version will give you better dispersion but gives up sensitivity.

I had a custom version built for our LS-6 and LS-9 models that utilized a dense felt on the front side like a pdr version but not on the back side. I also had them leave in all 5 rows of magnets to keep sensitivity high. Then I had them make me a 8 ohm diaphragm so that more of them could be paralleled and less of them in series. These are good from 800hz to 40kHz. The price is the same as a standard Neo 8.

Since you are using a metal cone woofer I wouldn't recommend running them up very high as they tend to ring in the upper ranges. I wouldn't want to push those past 2kHz. In fact they will sound much better if you can limit them to 1kHz or less.

The true ribbons really aren't capable of crossing that low as their power handling goes away quickly and distortion shoots up in a hurry if they exceed anything below the 2kHz range. They are also quite fragile, and I wouldn't recommend them in a line source application.

Danny Richie