HA, If that was that case, why come out with new amps and new internal designs? If there are no improvements in sound, just go buy the lowest priced version you can find and call it a day. Most people are not going to replace an amp if it doesn't sound better/different. I'm new to the ATI brand, but with Theta Dreadnaught, the I, II and D all have their own sonic character. With the I, II & III each having subtle improvements over the prior generation. I've not heard the D so no comment on that version.
Like I said earlier, this is my first amp from ATI so I am curious how it will compare to the amp it is replacing for my center and surround speakers, which was a McIntosh MC-207. Prior to the MC I used a Proceed Amp-5, which I found far more transparent than the McIntosh. I have a feeling the ATI is going to be far closer to the Proceed in sound. The ATI 3305 shipped yesterday, and I will have it Tuesday, which is great, as I can let it burn in over Thanksgiving.