My thought is that Atrium is a hybrid,,,not exactly stock; but not derived from source, either. Whatever you want to label it as, it's far, FAR better than anything THIS noob could pull off. I'm SOOOOOO wanting to learn this process, but need to teach myself a lot of stuff...not to mention get a working rig/rigs going to even be able to play around with!
Right now my daily driver is PT J.B.S 2.4. I've got 2.5 & SuperHelado on my sd card, as well as Atrium1.1; PartyTime 2.5 is not getting me MMS files, and that's a bummer for me because with a new grand-daughter, I'm receiving a LOT of pix. And Atrium is seriously wiggin' out with the GoogleNow update.