The GReddy 2-bolt flange is different from the stock flange on the ITR axle-back section. The ITR flange is like the other stock Honda flanges. The B pipe flange has a flexible gasket that seals into a cup on the axle-back flange, and the two are held together with bolts, springs, and nuts:

You may be able to get the stock ITR axle-back flange to bolt up to the GReddy piping, but I'm not sure if it'll seal properly, and you may have an exhaust leak(which is annoying). Let's say you got it to bolt up, the ITR is a 2dr(well, technically a hatch) and as you probably know 3rd gen 4dr Integra exhausts are longer than the 2dr ones, so the ITR axle-back's piping may not be long enough to clear your LCA and bumper.