The A/V-2 is a 4 ohm speaker while the A/V-3 is an 8 ohm speaker. The A/V-3 will also play lower so you won't have to play the sub up as high. The lower you can cross it the better the integration. Plus the transmission line design of the A/V-3 keeps really good control of the woofers. The A/V-3's don't need speaker stands either.
A/V-3 it is then, I'm definitely a fan of keeping the crossover to the sub as low as possible.
I wouldn't. Most of those active crossovers don't allow for any baffle step loss correction. Some will not allow for time delays between drivers that are caused by physical driver offset. Then you need more amplifiers to boot. It just isn't worth it.
Isn't there some pretty serious advantages in sound quality with active crossovers though? Assuming your unit doesn't do baffle step correction you can just leave that part of the network passive, inline with the drivers. Although that does somewhat defeat the purpose of going active.
I'd just heard that it was far superior to passive networks. Although I'm sure it makes a bigger difference with larger, power hungry speakers that are hard to drive.