As my HD700s also have a bit of a treble spike, I find the more subdued Lorenz to be a great match in my Glenn with GEC and the slotted Bendix graphite 6080 output tubes, both of which have good highs and lots of air . And I suspect that the more forward and airy Siemens might be a very good match with the more subdued Mullard 6080, but I haven't tried this combination yet....
Edit: OK, rolled in a pair of 1966 Mullard 6080 with Siemens C3g/s this evening for about an hour and quickly found myself listening to the music, not the equipment. :)
Given that the Mullard is typically considerably less expensive than the GEC and Bendix, it is my opinion that the Mullard 6080 together with the Siemens C3g/s offers a very satisfying compromise between affordability and performance.
Edited by gibosi - 4/17/15 at 9:57pm