I'll have to add Head-Fi and Headwize on the decent forums list if you're looking at headphone stuff. These guys go all out on headphone rigs like some do on speaker rigs. The guys on Headwize in particular are very helpful, especially with tube gear.I visit AK and DIYAudio often. AK people are very helpful.
As far as AA goes (I only look at the DIY Tubes section and Bottlehead forum), I've found that there seems to be a lot of bickering and such that goes on in the DIY area. Good info can be found if searched for, though, and there are a few that know their stuff and can be quite helpful with DIY questions, especially off-forum.