Hi Rafael, welcome to Audioholics.
You are right that "whatever sounds good to the listener should win". But that's within reason. Also remember that it's easy to fool yourself:
The first principle of scientific inquiry is that you must not fool yourself – and that you are the easiest person to fool. – Richard Feynman
It ain't what you don't know that gets you into trouble.
It's what you know for sure that just ain't so. – Mark Twain
It would be wrong to say, using the same single power supply to bi-amp is not ideal. It's accomplishes nothing at all.
I don't think you can send zone 2 signals to the amp section of your Denon AVR. The only way I know to bi-amp using an AVR is 1) you must have an AVR with pre-amp out jacks, and 2) you must have a separate amplifier with at least 2 channels. And quite frankly, you would do just as well with a more powerful separate amplifier without the more complex bi-amp wiring.
By the way, your interest in vertical vs. horizontal bi-amping is misdirected. Because bi-amping with an AVR can accomplish nothing, it can't matter how you arrange the wiring.