I successfully browse AW using various flavours of IE (8 at work, 9 at home, and 10 on my tablet). I've never had problems with the back button, but I don't use it that often. I tend to either use the "new posts" link at the top of the page, which shows you all the topics that have been updated since your last visit, or open up each subforum and thread I'm interested in as a new tab. Often I will keep the main page open so I can skip back to there.
There is also a "forum jump" function at the bottom of each page, which allows you to skip to particular boards without having to go back - and the breadcrumb trail above each thread is hyperlinked so you can go up and down levels within the boards too.
Browsing habits are a hard thing to break, and it's obviously a pain if you have to adopt different behaviour for only a couple of sites, but if you want to stick with IE9 then trying out alternative ways of getting around AW may alleviate some of your frustration.