IMO, it seems KJ-600 unfortunately still uses WJ-6, the annular intake is still there while I'm pretty sure AEP400/500 uses different intake as seen with models and the testbed. I wonder why they would still use WJ-6 despite the rumors about unsatisfactory performance of that model.
Well... what other broad category of reason could it be?
"Why aren't they using a new engine which is said to be better than an older engine" -- except for rare exceptions, the answer is generally always the same nature overall. I.e.; the new engine is not yet ready for prime time serial frontline use for whatever reason.
This, as far as I know AEP500 is fully ready but they are not using it. There were alot of claims previously about KJ-600 with AEP400/500 before as well.
PS: Or actually maybe it is AEP400 via this illustration