The ATI has good reviews, as does D-Sonic...
I would lean toward the ATI Class D because of the linear power supply. D-Sonic uses switching power supply like most of the Class D offerings.
I was wondering if I could use the older Aerial speakers and maybe change the tweet to the ScanSpeak Discovery
Changing tweeters is not necessarily recommended because they will have a different impedance curve and frequency response. This could throw the balance of the sound off a lot. That being said, in my opinion, surround speakers do not necessarily have to be perfect match. They should be close in sonic signature, but they are not as critical as matching left / center / right channels.