I’m sorry, but I apparently forgot to say that I don’t own a Sundara, so this is more based on what I’ve read about it. I was about to purchase it when the Elegia insane price of $400 hit last year and I’ve ended up changing to them.
From my understanding though, the Sundara is a headphone with tight and we’ll controlled bass, nice midrange and an airy and detailed treble. It has good imaging and a somewhat wide soundstage. I was specifically looking at it to contrast with my K712, that has a very wide soundstage but not that accurate, and it has more of a “bass hump” and less treble. The other two, again from what I’ve read here, are also more bass focused, with wide soundstage and a darker/recessed treble.
As for power, I think you should be fine for the most part. Maybe the modhouse Argons can max out your amp, as some people say they need a truckload of power. @WaveTheory has a great write up about the Zen CAN, maybe reading it can help you understand it’s strong points and limitations.