Haven't heard the vk5, but have owned the 5i and now 5se. Strength is liquid midrange, smooth highs and imaging. Weakness of the vk5i relative to the 5se is the bass tightness. BAT had a series of circuit board upgrades with the 5i. My impression that each probably improved transparency. A new set of any tubes can make a big difference. Best tubes are Tungsol 5881 and Amperex gp 7308's, all of which are pricey. Try to audition....
