As Wayne said, what you should aim for is flat response and phase alignment within a specific margin. EG: +/- 90degrees. This is something you can achieve with seperate horns. The concept of the unity is appealing and I'm sure Tom Danley's unity horn does sound very good, but you can achieve a system which sounds just as good by other means. But in answer to your question, I would not try it as a DIY project unless you have heaps of spare time, good measuring equipment and the money to try dozen's of combinations of different compression drivers and middrivers and xover configurations to get it right.