Best upgrade for the E88CC tubes for my Kora Pre?

I currently Telefunken and Siemens tubes and am wondering if there is a better tube and sonic differences. Any thoughts? Thanks.
Call Joe at JC Audio, he is the man for this. 925-229-2484
Good luck.
I have an Eclipse with the Siemens tubes. Better sound (richer) than the stock tubes, but I would have interest in what others have tried, too.
I started this inquiry and would like to pass on what I've found.
Someone mentioned "joe's tube lore" and he had quite an extensive cataloguing and evaluation of diifferent tubes. Going off of this and my own experimentation--Amperex 6dj8 PQ (premium quality) tubes made in US, white or orange lable, but definately the US made ones. They make the siemens tubes sound metalic and thin by comparison. I've bought a few at around 30 bucks or so a piece. Let me know what you think if you ever try 'em.

We like the Telefunken Falcon Grade, Siemens 7308's and Siemens CCa's. CCa's have great midrange but not quite as much bottom and top as the Telefunken or Siemens 7308's. Personal taste operative word in this regard. We didn't like the Amperex being to dry. The mullards were bloated in the middle and not much extension. IMHO We have sold quite a few Kora pieces and have experimented quite a bit. This does not mean that these tubes exibit these same qualities in all gear. Just our experiences with the Kora products.
Hope this helps