I think Sunn0))) is playing as well - I already deleted Conspiracy Records' newsletter that listed the tour dates (and I can't find it on their website), but if I recall correctly they're also doing an "Altar" show with Boris in London one or two days before ATP.
Martin a.k.a. "grain of salt" ;-)
Edit #1: at least one part of the above sentence is true -
http://www.atpfestival.com/events/at...p.php?view=940.
Edit #2: I'm completely right!
http://www.atpfestival.com/events/po...ad/line_up.php.