Well, I don't really base my listening on measurements but there are certain electrical properties that you can't ignore. If a tube doesn't provide enough power for the circuit as a whole, then it's kind of a nonstarter. In any case, yes, the TH900's are extremely efficient and I think my "crackling" sound may have more to do with overall gain than with microphonics. So I'm currently using an NOS Sylvania 5UR as the rectifier tube and some used RCA 6DE7's as the driver/power tubes. I'm looking for an NOS pair of something similar. The current result is a much cleaner sound with good bass and overall dynamics and no "crackling" sound at all. In fact, I'm listening right now to a John Abercrombie CD ("39 Steps") running through an Audio Note DAC 4.1x Balanced Signature into my WA6-SE with said tubes and then through a pair of Denon AH-D5000's modified with Moon Audio Black Dragon cabling, and am getting a very "tubey" sound that reminds me a lot of the Audio Note sound in general, using my AN-E SEC/Silver loudspeakers as a point of reference. It's definitely the case the Sophia Princess mesh plate rectifier tube is a (a) prettier than my Sylvania and (b) gives me a sense of a wider soundstage, but if I really wanted to get an ultra-clear sound with a super-wide soundstage and perfect image placement, I would probably go with a solidstate headphone amplifier, like the Bryston BHA-1. There's nothing wrong with that. It's just not the sound I'm looking for. I have a Blossom Blo-0299 solidstate balanced headphone amplifier with an auxiliary power supply driving a pair of balanced, Silver Dragon Sennheiser HD-800's that I use in my home office system for mastering high-resolution files and downsampling them to work with my Audio Note DAC, but I also have a Tri TRV-84HD tube headphone amplifier driving a pair of Audio Note AN-SPx modified AKG K701's that I use more for listening than for mastering again in my home office system.