IMO, if you're bent on running Lyr, I'd go with HD800, however that recommendation comes with a caveat: It applies if and only if you intend to EQ! The Lyr actually does sound very good with HE-6 contrary to knee-jerk reactions. But it doesn't drive it into it's "special" characteristics over the HE-500 that costs half as much. It's tonally smooth and balanced, but it lacks that extra bit of dynamics and detail that make the 6 special. It's not that you can't use it, it's that you can save a lot of money and get basically the same performance out of the 500s for that amp
I think 6W is into 30ohm. Or even less. It has power but it doesn't have the reserves for sustained current delivery and hit the dynamic swings on demand. I initially thought because the Lyr had balanced tone with HE-6 that it was fine in terms of the power equation but HE-6 just revealed how unrefined it is. HD800 proved me wrong, it's a lot more refined an amp than HE-6 makes it appear to be, indicating the "lack of refinement" is mostly due to the power requirements of HE-6. It sounds good....but it just doesn't sound much more special than HE-500.
Lyr's definitely a nice amp overall. It's not the best but it's darned good for the money. But it's still not powerful enough to make the most of HE-6. It gets a lot more out of HD800, and I had to do a lot of A/B tests between that and the 6004 with HD800 to determine where the 6004 shines better than it with HD800 (PM6004 is a $600 mass market speaker integrated and the HP out is just resistors off the main amp, so it's a class above Lyr both in terms of price and scale of economy from D&M...but it has issues with very quiet passages with HD800.)
HD800's a strange animal. The comfort and weight astound me...it's as comfortable as AD700! Maybe even moreso! Out of the box, the sound is every bit as putridly bright and harsh and irritating as I've always believed it to be. But with some time and care on EQ it can end up sounding more or less similar (as similar as it can be) to HE-6. The soundstage of HD800 is definitely wider, it sounds like it's coming from farther from the ear. However in terms of front image I found it benefits almost as much as HE-6 from some stereo image processing. HE-6 is smoother, HD800 is faster. HE-6 when fed well has got to be the king of bass...I don't mean "basshead bass" I mean smooth clean, hyper-detailed, fast bass straight to 20Hz. HD800 is suprisingly great at bass delivery to the point of almost rivaling HE-6, but the big planar driver simply wins at performing down low in ways the smaller dynamic can't. Conversely HD800 is a better champ at fine microdetail. HE-6 is darned good at that, but 800's speed gives it the edge on microdetail. I think they're more or less equals, but each wins in different areas, and ultimately both can be just as satisfying. If I had to pick just one...assuming EQ is allowed, if it was for listing to a full album or two in a session I think I'd take HE-6 and my big power amp. If it was for wearing it for hours on end, HD800 would win in a heartbeat due to the extreme comfort.
I actually like the PM6004 a lot with HD800, but unfortunately the annoying "crackle" type sounds (a very knowledgable lurker in this thread identified it as possibly being crossover distortion when below -40dB in signal level ) ruins it for classical, or any recording that has a large DR. I'm considering a Mjolnir to rectify that..... maybe.... it has the advantage of being a usable secondary amp for HE-6 as well though I suspect the big power amp will still handle them better.
Either way I don't think the difference is as night and day as "being blown away by a properly amped HE-6"....they're good...they're very good. They're smoother and ultimately more speaker like. Though HD800 isn't really that far behind in terms of speaker-likeness if EQd. I think a speaker afficianado would be more pleased with HE-6 as it will feel much more natural and familiar. HD800 may still come across as too "headphone sharp."
I really like both....I do think I prefer HE-6 overall. Possibly strongly. But I'm greatly enjoying HD800 almost as much.
IMO it's not so much a question of "better" so much as "preferred sound." In he bass region, they're technically better. In most other regions HD800 is technically better. If you like smooth natural speaker sound, HE-6 is the choice. If you don't care how much it presents itself like speakers....coin toss. If you don't have an EQ or some really warm tubes, run, don't walk, from HD800 HD800's strength is not it's sound signature, which is awful, it's that it's linear and responsive enough to take any sound signature you EQ it to have....much like HE-6...except HE-6's signature out of the box isn't nerve rattlingly awful like HD800 EQ'd (via an EQ or via tubes/amps/cables/pixie-dust) they can both be great!
Thanks IEM, great read as always. Plus you've persuaded me to stay well clear of the HD800's. I really don't think they're for me as I love the orthos sound too much