How to evaluate speakers?

To be a complete simpleton about this, forget about analyzing which does piano better, etc., etc, and focus on which speaker gets you off the most. It's a simple as that. Which is the one that causes you to want to stay up all night pulling out recording after recording and trying things you haven't listened to for years? Go with that one. There's some risk, but less so, I think.

For jazz I like to turn down the lights, close my eyes and imagine that the musicians are in the room with me. Each instrument has it's spacial position, lot's of "air" around it, and realistic sound. Piano, string bass, horn, drums. That's a good speaker/system.

The second aspect is toe-tapping. With some speakers, my foot just ends up moving to the beat. I like that.

The third aspect is listener fatigue. I want a speaker that I can turn up and listen to loudly when I feel like it without having my ears start to hurt.

Hope this helps. If you can't decide, that means that both speakers are pretty good!

Depends. If your speaker outputs are wired in series or parallel. If series, yes it will make a sonic difference, with the "B" speakers sounding worse. The owners manual might be of some help in answering this.