I have wondered the same thing myself. They went to dual transformers to save space (allow the amp modules to be longer) as a single transformer would have been thicker.

Acurus made some of their home theater amps stronger for the front L/R channels. How to best do that, however, is open to some debate. I'm not sure I'd put both front channels on one transformer.

I've designed audio power amps (I'm an audio engineer) and I'd be tempted to split each front L/R channel onto its own transformer. That way the amp acts more like a true dual monoblock unit in stereo mode. You will have less interaction between the stereo channels and more power available. In this scenario, one transformer would be burdened by the extra bias/quiescent current of the extra unused amp module but I don't think that would really affect things much.

In 5 channel use, the center channel usually works the hardest. So you'd ideally want it on the transformer with only two channels. So I'd probably put say the front L and Center on one transformer and both surrounds and the front R on the other.

If you run your system in say a 5 channel "equal power" music mode, the three channels that are sharing one transformer are going to clip slightly sooner than the other two. Still, under most conditions, we're probably talking about less than 1db of peak power differential regardless of how you split the channels up (as long as the transformers each have a high enough VA rating to stay out of saturation running three channels with fairly normal speaker loads). With really reactive low impedance speakers (which place far heavier demands on the power supply), you might run into some audible problems, however.

The whole debate about sharing a single transformer (like ATI does) or using a transformer for each channel (like Sherbourn does) is a tough one. The more transformers you have, the more likely you are to have some mechanical noise/hum. Also, one channel cannot borrow from the current reserves of another (beyond sharing the 120 volt primary winding of the transformer) so you typically have lower dynamic headroom.

The advantage to individual transformers, of course, is the amp behaves pretty much as a bunch of monoblocks. You get better channel separation and virtually identical power from each channel regardless of the load on the other channels.

So... hopefully that sheds some light on things? If someone wants to pop the top off their 755, it should be fairly easy to trace the wires out of the transformers and see how they split the channels up. You can then connect things up however you'd like.