I'm using an Alpine F407 to run the Vifas and the Neo8s right now. 140W x 4, or about 75W x 4 rms. I wouldn't want to give them too much more, as they are fairly efficient and allow me to set the gain fairly low. I have them crossed at 60Hz, and they don't seem to have any major weakpoints in thier current range (60-4000Hz) I'll eventually be using them to cover 60-800Hz, and have the Neo8s cover 800-6000Hz, allowing them to truly shine.
I wouldn't cross them over under 60Hz, for that I'd look into a larger driver
