[Trae]

Equipment:
SMSL M8
Gustard H10 for headphones
Emotiva Mini-X a100 for headspeakers
Various music (mp3s of various bitrates and flac) - classical, electronic, r&b, Chesky demonstration cd
 

HD800
Very detailed
Cold sound signature
Soundstage is diffuse sounding
Easy to hear or pick up subtle sounds
Mids sound thin
This would be a cup of ice cold water with lemon
 

K7XX
Basically sounds like the HD800 but with a warmer tonality and more centralized imaging, which I believe is due to the distance the drivers are from your ears.
The interior of the HD800s form a cup of sorts, and the K7XX's drivers are pretty much right against your ears. You can get HD800-esque results by slightly pulling the headphones away from your ears.
Overall, I enjoyed this headphone more than HD800
Mids are more realistic sounding, but still on the thin side
This would be a cup of lemon water at room temperature (read warmer)
 

Frankenheiser LCD-K1000
Tonality-wise, the complete opposite of the HD800.
Extremely warm and involving
Would describe the sound as natual and euphonic
Due to the thick and dark sound signature (compared to HD800 and K7XX), it is harder to pick up subtle sounds than with the HD800 and K7XX.
Soundstage does compete with the HD800, but it has a very unique speaker-like presentation. The soundstage is wider, and depth is about the same.
Imaging is also very good, though I'd give the upper hand to the HD800 there.
Bass performance is on another level. Punchy, clean. The best way I can describe it is the bass sounds invisible, like it comes out of nowhere.
This would be a smoothie. A banana smoothie because bananas are tasty.
 
But the big shocker for me is how close the K7XX and HD800 sound. I was honestly expecting a larger gap, and I would have no problem recommending the K7XXs over the HD800s. The sound signature is slightly warmer, and you get basically 95% of what the HD800 has when it comes to SQ for a good bit less cash. If the HD800S is warmer than the non-s with the treble worked out, I would say the K7XX would be closer to those in sound signature than to the HD800.
 
EDIT: If I'm too vague on some things, let me know if you wanna know more. I just wanted to make a quick general impression of these headphones for you guys.

 

[AzraelDarkangel]

LOL! Nice! I thought about doing almost exactly the same thing with mini full range 2-3" speakers. I even narrowed down my selection of drivers but never got around to trying it. Btw, did you upgrade the op-amps in the Gustard yet?

 

[Trae]

Just keep in mind that you might be doing a lot of tweaking to get them to sound right. Putting speakers in a design like mine is sorta like putting a -8dB high-shelf filter on them, along with some newfound resonances and other peculiarities. I'm using 4 25ohm resistors through all wires to cut down the noise on the amp as well as a weird 60 cycle hum the amp has (it travels from the left to the right channel the more you twist the volume knob. Can't hear it now, though), and I have 6 parametric equalizers in foobar to make them listenable. Two for balancing the FR, one for balancing L/R, two for different types of bass boost (low, medium, enable both for high- review was done on medium), and one for gain.
 
No...this is the first time I have seriously used the Gustard in about a year. Need to sell the thing because it's not really benefiting anyone by sitting in my closet.
 
But for those who want to know, it can drive the AKGs and Senns very well. You might have to flip the gain DIP switches, though. With some, uh, volume tweaking, you could blow the drivers in both headphones with this amp.