Best tubes for BAT VK5i, help please

Want to upgrade to some better tubes for my BAT VK5i. I don't want to spend the 2K for the SE series and I think I can improve the sound with a tube change out. Any comments as to where I can go or who to call for advise would be very much appreciated. Thanks to all.
You can call Kevin at Upscale Audio for tube recommendations. However, he may not sell any of the very best NOS tubes to you because BATs are know to be hard on NOS tubes. He can, however, recommend and sell some great new tubes for the BAT VK5i.
Hello Metaphysics:

First I've heard of BAT being hard on tubes, I find the opposite to be true, perhaps you can elaborate?

I have a 5i. I think its soft start feature is supposed to make it less hard on tubes than many other preamps, but I've never tried anything but the Sovteks.

I've heard that the Amperex/Tungsol combination is supposed to be "the" combo to use with the 5i. Kevin can hook you up, but he's be no means the cheapest supplier around. Good luck.
Paul, I'm only going by what Kevin told me. He would not sell me NOS tubes for this stated reason. Not sure of the validity.
I bought NOS from Kevin a few yrs back. 6 Amperex gp 7308's (there are 2 positions that aren't critical to the sound) and 2 Tungsol 5881's. They lasted for 2-3 yrs. I've been running the 7308's in the vk5d just fine. You might want to try the older version of the Sovtek 6992 he carries. BTW, Steve at BAT had no problem with using NOS, but I believe Viktor likes the Sovteks.