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?
I tried a pair of Telefunken 12AX7 my friend brought over, and we both liked the stock tubes best, also. It was kind of surprising, as he has tried A LOT of 12AX7, and thinks the Telefunkens are best. Still, the pair he brought over may not have been the best(we pulled them from a Sherwood amp he brought over), so we were unsure of their lineage.

Someone once wrote to me that the Telefunkens made a nice difference in their JOR. Another wrote to me that 5751 improved the sound. But, again, the originals sounded best to me so far. Not that they are the best...

I doubt you would need to rebias, I didn't. But, I didn't check to see if it affected it either.
Thanks Mr. Trelja to all your helps.

As soon as i can i will try the Mullards 10M or the Telefunkens ECC803S.

After i will told you (and to every interested Audiogoners)how do they sound in the JOR.

Best regards,