Running your CV's full range would be more taxing on your receiver than the M80's I believe due to the woofers on the CV. I'm not sure of the CV's efficiency rating but the M80's are very efficient.
Once you get the M80's and new sub, the sub will be self powered freeing up watts/power for the mains as running the M80's small or with bass management would redirect low frequencies to the sub.
One of the design goals that is very common among Cerwin Vega speakers is their efficiency - very easy to power. If I was a wagering man, without even knowing the specs of the CV's I bet they are more efficient than the M80's.
