Alan,it appears that the engineering has in fact changed. Although it's fashionable in some circles to poo-poo the THX certification as a mere marketing move, some of those who've gone through it have reported on the technical changes that have had to be made, reportedly including the ability to drive a 3.6 ohm load. Also, Yamaha at least claims increased current handling capacity, etc. Only time will tell, I suppose.

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Enjoy the music, not the equipment.