Martyn; I also a pair of keltiks,also 4 klouts,Ikemi,5103,I can only speak for my own personal experince,I up graded the tweeters and the mid-range,and I was very satisfied.In my room aucoutics,the tweeters seemed to be more open,more detailed,highs were just cleaner,and the mid-range,was a vast improvement.This is only my own experince,Hector seems to hear something different,but in my case it seems to have made a improvement. good luck in what ever you choose.
Douglas