Now I will have to buy 2 more surround speakers for a 7.1 setup so I can listen to DTS-ES.
Rather than buy two more speaker, why not put that money into a blu-ray player so that you can listen to DTS-Master HD audio, which you can listen to in 5.1. As to the sub crossover, you can cross it over where ever you like. It doesn't have to be a THX cerified sub to cross over at 80hz. Just experiment and see where it sounds the best and best integrates with your other speakers.