I would try Shunyata Anaconda Helix Alpha PC if I were you. It should give some more HF air and sparkle. This the cable that ARC uses at their factory to voice their products. I use Anacondas myself and are very pleased with the result.
You should also try to put the pre on some footers. I have tried Finite Elemente Ceraballs (rigid) on my Ref 3 but finally settled on Sorbothane feet. The improvement is not subtle.
Last but not lest, you may want to try NOS 6H30-DR tubes (you have only 2 in there, so the investment is minimal) which offer slightly beter deninition and resolution. Do not forget to get Herbie's UltraSonic-9 tube dampers for them.