Thanks for your feedback! I am a little bit curious as to exactly why you think replicating the XRT2K concept is a bad idea? I know there are issues connected to obstructing the woofer-line like this, but as it works for McIntosh it should surely be possible to replicate? Or am I missing something?

As for the RD75, I agree that this is not perfect. Sensitivity is a bit low, it rolls of too early towards the top and it costs more than a line of shorter drivers outperforming it in the top octaves. However, if I am to attempt this design I can't really see any alternatives - crossing as low as I have to (below 400) means smaller ribbons and planars are out. And, I am hopeful that the RD75 (even with all its limitations) with the help of some EQ could sound very good given the reports I have read on it.

BTW; Thanks for the link to the images - some interesting designs there! One I have not seen before is http://home.pacbell.net/lordpk/speaker/26.jpg. Do you know what drivers have been used in this one?