Morganc - mainly just upgrading the resistors to be able to be handle big power, caps, increased internal dampening... and the more versatle 8ohm.
Rcduck7 - the class D pro amp is doing everything you said. I am running a single CROWN XLS 2500 (over 700! guaranteed watts into 4ohms). One thing I REALLY like is the rich, deep, but extremely articulate bass at the lower volumes. This amp really has a tremendous grip on the drivers. CRANK it up and it is crystal clear - almost deceptive in that it doesn't seem as loud as it is! I am not missing my tubes right now. Getting better and better as the hours build up on this amp.
Rcduck7 - the class D pro amp is doing everything you said. I am running a single CROWN XLS 2500 (over 700! guaranteed watts into 4ohms). One thing I REALLY like is the rich, deep, but extremely articulate bass at the lower volumes. This amp really has a tremendous grip on the drivers. CRANK it up and it is crystal clear - almost deceptive in that it doesn't seem as loud as it is! I am not missing my tubes right now. Getting better and better as the hours build up on this amp.