The hum is audible through the speakers and as i previously mentioned, it kind of sounds like electrical current through overhead lighting, but not that loud.
The noise floor from the preamp 'drowns' out the hum once it is turned on but that doesn't mean the hum isn't there.
As for the heat, i'm sure the difference is in the weight/size of the heatsinks. The A23 is 28lbs, the Stratos is over 50.
I really like the Halo features though which the Stratos does not have.
Deciding between what makes a difference and what really won't is killing me.
There is still one unit left on my short list though, the Anthem MCA20
The price for it locally is $1500cdn plus 14% tax. I can get it from the States for $750usd (add shipping, customs, exchange and tax) and the equivalent Cdn is under $1300.
Goes to show how much the audio vendors really jack up the prices.