Best Preamp Tube 12AX7 for Jadis Orchestra Ref

I´m scearching for the best ECC83/12AX7/7025 tube for my Jadis Orchestra Reference.

I have the following ones:
-orignal ECC83/12AX7 (silver plates)
-Telefunken ECC83/12AX7, NOS, soomth plates
-Amperex orangle globe ECC83/12AX7
-Amperexe Bugle Boy ECC83/12AX7, NOS, holland

For my tastes the original pair have the best sound than the rest, but i will apreciate best midrange and a little more of bass extension.

The power tubes are Ei KT90 (type III).

One more question: when i replace the preamp tubes i need to rebias my amp?

Anyone can help me?
Acccruz