NOS Tubes for a Newbie with Antique Sound Labs

I've recently purchased a new system comprised of the ASL AQ1001 DT integrated amp, Von Schweikert VR-2s, and Rega Apollo Cd. I've read, and been told, that replacing the 12au7 pre-amp tubes is the best bang for the buck. I like the sound of my system a lot. Friends of mine, who have more of an ear than me, are impressed with the sound, but add it rolls off a little on the high. I was told the ASL tends to remind them of an older Dynaco amp - if that helps - i.e. it sounds like antique tube equipment. I am inclined to look for tubes that might provide more detail in the upper-end. Again, the sytem already sounds warm, so that's covered. Any thoughts are appreciated. By the way, if anyone has experimented with different power tubes, I'd be interested as well.
RFT, Tungsram, Sylvania are all good, solid, inexpensive 12au7 tubes. I have also been told Mazda tubes are worth a try.
RFT is what I am using, I think they are better than anything I have tried. Trying to get agreement on which tube to use is like trying to get agreement on which power amp to use. Or malt scotch. or wine. or.....
Sounds like the Telefunken or Siemens 12au7s might do the trick.
Thank you for the input.
Telefunkens are always the best all around tube. Amperex may be too laid back in the highs. I prefer mullards. If you want to try less expensive NOS, GE's can be great-very lively, just not as smooth. New tubes-I like Svetlana