Pre-amp tube upgrades?

I am presently using a BAT VKP10 for my phono pre and an ARC Ref 2 for my main pre. The phono is a Mithcell Orbe with an SME IV.V and a Koetsu Black. I'd like to begin experimenting with potential tube upgrades. It is already by far the best sounding combo I've owned, but for the past 35 years I've enganged in the never ending search for a better sounding system. Any suggestions?
Hi Jwin,

Sorry, I don't have a specific tube recommendation for you besides try different tubes in your ARC. JoeS' article on 6DJ8/6922/7308 tube family on Audio Asylum site has a lot of good information. I have an LS-1 and an LS-2B MkII, I prefer Amperex tubes in these.

I do have a question for you regarding the Koetsu cart on your Orbe. Can you tell me more about how you like it? I currently have a Benz M2 on SME V on my Orbe SE.
Gundam91- The Koetsu is a great match for the SME arm. The Analog Room in San Jose did a great job with that suggestion. It is a low output MC cartridge and requires considerable gain. I employ the step up transformer funtion in the VKP10 at maiximum amplification. If I remeber correctly its about 68db. The bottom line is its extremely musical and a big improvement over my Clearaudio Virtuoso.
The tubes, you use, will ultimately determine, the sonics. There are rich warm tubes, Telefunken, Mullards, and lean, detailed tubes, Siemens. In both the pieces, you named, one would only need to insert, 2-4 tubes, to change the sonics, as these stages, influence, the sonics, the most. Only actual experimentation, will determine, which tubes, you will prefer. If you seriously wish to know, my advice, is to start with a pair, of Telefunkens, and Siemens each, since this represents, opposites ends, of the premium tubes, sonics. Place them in the first gain stages, and listen, to each. Then, you will know, which direction, to head in. BEWARE, tube rolling is contageous. With most premium tubes, you will always get beautiful sonics, it will just depend, on which you like best, and that can change, from day, to day, recording, to recording, mood,to mood, etc.