If you like the VK-5i then it seems to me you will not like the Line 3. The VK5i involves you in the music and is forward in the true sense of that term (ie. not bright, but images are in front of the speakers) which is a matter of taste. When you use all the usual listening criteria the line 3 impresses, but when you try to boogie to the music there is curiously something missing. This is a very controversial topic, but for me the Line 3 has no obvious flaw except that it is boring musically. And no I do not like colorations instead. It is about the way the notes start and stop that means the rhythm in the music does not engage you. Apologies to Keis - I can very well imagine the beneficial effects of a Line 3 on the Krell/Thiel combination, and it may well be that the liveliness of the Krell and Thiel overcome what I hear as the Line 3's faults. Owning a pair of 3.6s myself I am utterly sympathetic to the quest to tame its flaws and enjoy its magnificent attributes - but it is not easy.
