Everyone should send Skylab $20.00 for research and time, since he has done the largest portion of leg work.
I attempt to match the best sounding tube to a particular headphone, since it seems, to my ears anyway, that different tubes add SQ attributes to a specific HP. For example, DM-5000's doesn't display the upper frequency sibelance when utilizing the Mullard IEC 6DJ8 ECC88 (warmer sounding tube) vs the Lorenz PDJ8 PCC88, which compliment the laid back sound of the HiFiMan HE-500's present.
I would really like to purchase a pair of Siemens & Halske CCa gray plates, but at the current asking price (NOS) I'm going to roll a bank before that comes to fruition.
Rope