Tuxmachines have made this tutorial with Kanotix, which is very close to stock Debian Sid. So they think it'll work on stock Debian Sid.
Read it here
So why not run AIGLX with the ATI driver? Because, as far as I can tell, the proprietary ATI driver doesn't support the “composite” extension. Evidently you can run AIGLX using the non-proprietary “radeon” driver, but it's much slower. So, on my laptop, which has an ATI Radeon Xpress 200M, for example, if I want those fancy desktop effects, I'm stuck with Xgl.