The 8.A pulls ahead on soundstage. The 4.Ai is a small, intimate jazz club where the 8.A can do a full size stadium if you'd like. Rammstein's Völkerball sounds huge. The 8.A has a slightly more rounded flavor to it, without ever sounding rolled off or sacrificing details. When listening to Keith Jarrett's The Köln Concert the 4.Ai pinpoints exactly who in the audience is clearing his throat and that more than one person does it during the concert. The 8.A lets me know that somebody cleared their throats and if I listen for it, I can tell you where they're seated. All the detail is still there, but not served on a silver platter like the 4.Ai does. That album and stuff like Eric Clapton Unplugged is where I prefer the 4.Ai. The intimate feel and all the micro details done so well by the 4.Ai really makes those recordings come to life.
When it comes to bass, the 8.A is as good as it gets. They have no problems at all matching the depth and impact from bass monsters like the FS Atrio Mg7 and the ATH-Pro700 mk II while outshining them in both texture and control. But only if it's in the music. Some of the EDM stuff I enjoyed with the Atrios sounded a bit flatter on the 8.A than I was used to, so I thought the didn't go as deep as the Atrios. Then, when listening to the soundtrack for The Dark Knight, specifically the track "Why So Serious?" I found out that the 8.A goes deep - real deep. But unlike the Atrios, the 8.A does it only if it's in the music. The 4.Ai will are great at reproducing the sound of drums but don't hit you with the same visceral energy as the 8.A and they don't go as deep either. For those of you with the 3.Ai: Notice those huge bass drivers in the 3.Ai, twice the size of the mid- and treble units? Yeah those. The 8.A has two of those for each side.