Blackie:
There is a fairly comprehensive posting on this. The N803s are excellent speakers, and you will ENJOY them: currently, I have the N802s all around: the only difference is the N802s provide more bass: you subwoofer, if you have one, will augment the 803s in a substantive way (I have the ASW 4000, and it seamlessly melds with the Nautilus line).
My amps are B&K 4420M monoblocks: 250wpc, and they are plenty for the 802s. My recommendation is to stay in the 200-250wpc range, and ensure that you have at least a mid-fi manufacturer: B&K, Bryston, Aragon: to name only a few.
The Nautilus line is unforgiving on Source electronics: CD & DVD Players, primarily, and will benefit from assured power: but there is no need to go overboard.
If I can help in any way, post back.
mdorsam