Cayin A-50T - Tube Upgrades??

I recently acquired a Cayin A-50T with all stock tubes, and very low hours of use. I do want to try some different tubes at some point in time, but only after I feel that it is broken in. Since I have quite a few 12AX7's and 12AU7's, I am reluctant to purchase any others unless there is something that would be far superior to what I have. Also, I do not have any extra EL34 quads, only some different type pairs, so I will look to purchase some new production EL34's, as I just don't care to spend what it will take for a NOS quad.

This will be my first experience with a tube amp, as I have always used SS integrated amps. Here's what I have for 12AX7's and 12AU7's,

GE, long ribbed plate
RCA, grey plates and black plates
Raytheon, black plates
Sylvania, long plates and short plates
Mullard, short plates and box plates
Telefunken, smooth and ribbed plates

Any suggestions for EL34's and which tubes should I try first?

Comments will be greatly appreciated.
Ilove the New Sensor Mullard EL34 in my Primaluna

if you like a warm sound use the mullards
I'll go with the Winged "C" (SED) EL34.
I agree completely with the above EL34 reccomendations... depending on your 'choice' of sound... EL34's are very warm and rich in the mid range.. If you want a bit more 'crunch' a la' KT88... try some KT77's, they are a plug in replacement I have been running 77's in my EL34 based amp for almost 4 yrs!
Try EH 6ca7 for a fuller and tighter bass. When you have more budget, you really should try the shuguang black treasure 6ca7z better top end extension. I stopped rolling power tubes ever since i tried the black treasures. btw i'm still using the cayin a-50t.
I'm using Pavenes and Black Treasures throughout my system at the moment (except in my Shindo pre which I have no intentions of rolling tubes in) and they are pretty darn good tubes. They aren't where I'd look for lush, warm and euphonic, but they're linear, clear, full and resolved.

BT tubes can be had for significantly less then their retail pricing from a number of reliable sources if you don't mind shipping directly from China--like $93 a pair for the 6ca7-zs.