I came across a couple of options to go with on the V6 and V7 tubes:
RCA 6189 Triple, Mica Black plates.
Also found a Tesla, NOS Tesla ECC802S , superbly musical and detailed tube.
Have been told that Both are absolute top of the line when it comes to sound with RCA being warmer, but Tesla being more liquid.
The dealer will let me try them both in my amp, if I like them, I purchase, if not, I send them back.
I will stay with the KT88 -C SED for now and see how the preamps make a difference.
My current sound is good but I have the urge and feeling that other tubes can take me further, giving me more detailed sound image, a very transaparent and very musical image.
On my Ayon and Mac system, I was succesful with tube rolling (this is my other system in a different room, its a CD system, where I use Ayon 5S CD player, all tubes with Dynaudio C4 and Mac amps).