Cary SLP 05 - Mixing Phase Splitter Tubes

Hi

After a long trial and error process (also replacing the power cord with a Sablon Audio Robusto), I may have arrived at the combination of 6SN7 tubes that work best in my system. It has taken a long long time and I would like to thank many of the guys here who helped with their comments, especially Rodman.

What I ended up with is:

Tubes 1 & 2 (the front two tubes from the left)(L & R channel positive phase gain – buffers) - RCA Grey Glass 6SN7 GT

Tubes 4 & 5 (the back two tubes from the left)(L & R channel negative phase gain – buffers) - National Union Black Glass 6SN7 GT

Tubes 3 & 6 (the front and back tubes on the third column from the left)(L & R channel balanced input buffers) - RCA Grey Glass 6SN7 GT

My question now is can I mix the phase splitter tube pairs with different brands as I have so that the positive phase gain tubes are one brand and the negative phase gain tubes are another? I like these results the best so far except for some sibilance in the treble which I didn't have when I used the same brand ie. all RCA Grey Glass. Is this damaging?

Occasionally, the sibilance sounds like minor clipping but this cannot be the result of insufficient current driving the speakers because there is plenty to spare.

Thanks