Jafant,
You will have to ask Bill or Lew the specific reasons why these two products were released in the same time period at the upcoming CES show in January. I believe that they were appealing to two different markets: the CT-5 to the A.R.T. inclined crown, and the CT-6 to the budget/high-end crowd, where CJ has always excelled IMO but seldom sells enough units to be profitable.
Both amps are excellent. But in my opinion the CT-6 is simply too close to the sound of the CT-5, compared to the difference in original price. It's an even better bargain now, as the street price seems to have depreciated a little more than the CT-5.
I wouldn't kick either one out of bed.