Upgrade BAT VK-55 to VK-55SE? Worth it?

I have had a VK-55 for about 3 years now. Excellent amp that I have not been able to better no matter how hard I try. I am really happy with it, but have been considering having BAT upgrade it to the 55SE. $2K seems pretty pricey for the upgrade. I have never heard the 55SE in person, so it is hard to decide if it would be a worthy upgrade. Has anyone compared the two directly? Is there a significant difference, or a small incremental gain in performance?