AE or Spec-R gear diff is similar in quality; AE is JUST SLIGHTLY better built. Some of the older Spec-R units have issues where the outdrives are too tight for the AE blades, but they can be filed down to fix that.
To be honest though, if you're thinking of changing to gear diff in an effort to reduce chatter, it may be counter-productive. As Rick pointed out, the chatter does not really affect the car under load and when the suspension is settled.
Changing from front spool to gear diff will also alter the handling characteristics (maybe what you're looking for, depending on where you run). Generally, gear diff in the front will give you more steering, but less power out of the turns. Spool yields the opposite results, so tune accordingly.
If the symptom you're describing with the CVA is more severe than just chatter, they may need to be rebuilt?
To help you make a more informed decision, it's also worth mentioning a new gear diff is almost the same cost as a set of DCJs.