Yes thats the downpipe in question. There's a few pictures around here of it installed, it requires some minor modding to fit as it is intended for the BP. I actually just got ahold of a used one myself, they're a really nice piece (2.5" right off the turbo, divorced wastegate, and mandrel bent all the way) If you can afford it - it'd save a lot of work. I'm unaware of any other aftermarket downpipes. (I heard at one time Midco had one? but 2.25" comes to mind?)
I'm not sure that the oil pan has enough clearance for a 3" pipe. You'll have to grab some measurements, my concern is oilpan to subframe clearance. I've seen a 3" downpipe on a GTX before, but it was a full custom turbo setup.
I mean, the stock turbine housing's outlet is less than 2" in diameter, the turbo itself is a massive restriction for big power. 3" is overkill and I honestly think you'll see major boost creep with it, be sure to port the hell out of the wastegate.
I enjoy having the active exhaust on my car, but at the same time its not too often that I touch it. Its not my daily driver anymore so I guess I don't drive it as much. I've driven Russ's Super Roo a lot and he has Magnaflow mufflers, which are quiet-ish at idle but loud, and oooooh so sexy under throttle. I'm seriously considering one or a set of those in the future, with no cutout.
I see a 2.5" cutout on their site too. Looks like a nice piece, and inexpensive...hmmm. I enjoy my converted throttlebody but I'll keep this in mind for future projects...
My $.02 anyways
-Rocket