I've built 2 AT's and they're on a different planet from direct radiators altogether. The first one I built I initially A/B'd with one of my PA Bins (600w Ported 18"). Driven with a 550w into 8ohm power amp, I pushed the AT pretty hard. Not hard enough to do any damage but enough to shift some air - I was really impressed at how low and clean it was - and how easily it kept up with the 18"!!!. It really is on a different level from a typical "put a speaker in a box" set up, but your just going to have to trust what you've been reading on this site and go for it.
One final point is that I spent £85 in total for the driver and all materials including a S/H americans warriors car amp off eBay (120W Mono) - I guess that's about $165 at today's rates. When I showed it to the local ICE specialist they were a) very impressed with the sound b) confused at how an 8" driver could go so loud and low c) Unable to come up with anything that could begin to compete with it unless I wanted to spend in the region of £200 for a bigger driver and double that for an amp....
Build one - you'll never go back!!! Bill...I salute you
