The A/V-3 is the successor to the A/V-2; it uses similar woofers (although a 16-ohm variety that are easier to drive) and the same tweeter. However, the A/V-3 is a floor stander and uses a transmission line design to increase the bass output. If you want to know how transmission lines work, that's beyond me. But they're cool :)
The A/V-3 is probably a better deal than the A/V-2, because when they both have a Sonicap upgrade (recommended) the A/V-3 actually costs the same or less than the -2. It takes up the same amount of space, since you'd have to put the A/V-2 on a stand anyway. It's a bit more work to build the cabinet, though.
There aren't a lot of reviews out yet since the kit is relatively new (end of 2003), but searching in a few forums should yield some good opinions. All praise so far.
Designer Danny Ritchie is a very friendly guy and a frequent forum contributor.
The kit includes all of the parts you'll need except the cabinet; you can buy those in various states of assembly as well but they aren't cheap (because they're big, and take a lot of work). The Sonicap upgrade is recommended; the Blackhole upgrade is optional and somewhat debated (PartsExpress
? damping sheets + mattress foam stuff seems to do the trick). Search the forums for more information about those.
This is available in a sealed, shielded, sideways variety to act as a center channel; I don't know much about that variation.
The kit can be found at
https://www.gr-research.com/performer/av3.htm
