My original 2005.2 sub suffered from the problem that you'll see elsewhere and I replaced it with a KUBE 2 from the current 2005 series bundle. It works well with the original sat speakers so maybe worth an audition.
ÿThat's the key thing I'd suggest - have a listen to any candidates as I've found you can't buy subs from reviews alone!ÿ
Hi ajeffo, This is the question i asked my local independent shop Acton Gate Audio and he said the Sub that comes with the kef 2005.3 will be compatible.