Sorry for being slow to chime in on this one, but I was out of town... Ah the Ritz-Carlton Naples beach....
I currently run the Canton Vento 809's with and 805, 802's and 850 sub as my reference system. Great speakers, I haven't yet heard the 890's but spoke with Frank Gobl their designer who tells me they are pretty similar, so I can give you my experience here.
First, as usual, Jerry is right about power. I personally think you could drive the Vento's with 100wpc, but they would not be able to reproduce volume or dynamics well, even Canton recomends closer to 200 wpc, and they can handle more. I had been running mine with a Proceed HPA-3 and HPA-2 in the review I did of them for the magazine.
They ate up the 250 wpc these amps put out (actually when these amps are bench tested they usually output ~325 wpc) with ease. I also did the reviews of the Sunfire TGP V and TGA 7400 amp, which I used with the Vento's.
The Vento's have a warm and slightly laid back sound, which I love about them, but that can be changed by amplifier choice to your tastes. The Bel Canto's Jerry speaks of are lush and warm and for me would be an ideal match for the Vento's, I haven't heard the NuForce's yet, but from second hand reports they are similar.
You won't be unhappy with the Sunfire amps either, though the 5200 might sound a little thin on a power hungry speaker like the Vento's.