Have not lived with them but have heard both. I'd be rather surprised if you didn't find the 96 a considerable upgrade over the 9. IME, the 93 comes pretty close to the 96, and I would chose it over the 96 on grounds of bang fer buck.
Ladok, Your right, it seems I may be the only person that has noticed this all though as you mention, the reviews do note having to dial in the bass. Hope you can give them a listen before pulling the trigger. You'll get a larger scale with these verse the Nines. I was struck by how rich and visceral the 96's sound. They make my E's sound polite by comparison but I just was not totally feeling their groove on the times I heard them. I've not heard that issue with the Nines or the E's.
I own O 96's and Shindo amps (Monbrison and Haut Brion) and would definitely say they groove. Wonderful combination with shindo. The bass can be tuned with positioning but its different to the bass on the gibbons. The bass isn't tight yet I wouldn't call it loose. Its weighty and has character and color to it. I love the bass on them.
Well, I very definitely want to "feel the groove." The Gibbon 9s do this very nicely. I've got plenty of room from the side walls to "dial in" the bass. I would not want to give up boogie factor to get bigger scale and deeper bass, or the sense that the music is independent of the physical speaker box. Actually, I'd like it all, including reasonable sensitivity/high impedence (tube friendly).
My system has some of the most boogie factor I have ever heard and I have heard quite a bit, so the O96 can get the toes tapping it is one of there strengths and the things I like most about them. But my Garrard 301 and shindo's certainly help as well with those aspects. Its the density of tone and biggness of sound that is the major upgrade from gibbons. But if you are more into pinpoint images then I would imagine Gibbon X's might be more your thing.