I brought my Omega 2 setup to my friend's reference system and we did a shootout with the K1000.
Source: Naim CD555 and power supply (we used digital mostly because it is easier than vinyl when doing lots of music changing)
Preamp: modified EAR 864
Power amps: custom built 300B/ECC99 monoblocks, WE300B
Headphone amp: Headamp Blue Hawaii, EH tubes
Cables: Kimber Kable, Crystal Cable, Stealth, don't know exact details
Headphones: AKG K1000 (11xxx sn), Omega 2 MK1 (both stock)
Speakers: Avantgarde Duo 2.1
The Blue Hawaii was run from the loop out of the preamp. The K1000 connected directly to the monoblocks using the extension. These are reference amps and many 300B amps came and went out of his system before he settled on these.
For music we mostly listened to well and not so well recorded post romantic era classical. With a mix of some first Japan pressing jazz discs (CP32 and TOCJ) and first pressing classic rock from Europe and Japan.
The K1000 are owned by my friend, but I've owned them several times and know their sound. He has only heard my Omega 2 on a few occasions.
The most obvious difference that we both noticed between the two was the difference in bass and midrange detail. With regard to the midrange, this is especially evident with the symphonies. And bass becomes even more obvious with all three types of music. The K1000 was obscuring midrange micro detail in many of the symphony pieces that couldn't be heard even if we took the volume past the control level (matched with digital RatShack meter). One very obvious example is the 1959 Bernstein/Mahler/S5 on Sony Classical label- during very loud and dynamic passages a single violin is completely buried in the mix with the K1000. Switching to the Omega 2this softly played violin is heard in the distance.
I suppose picking out these micro details becomes easier with the Omega 2 because the O2 paints a convincing portrait of a concert hall. So a sound played very far away is heard far away and appropriately "muted" (softer). The K1000 has a more difficult time with these complex depth cues and details and on really dynamic passages can tend to have the wall of sound effect. These midrange issues become less obvious with studio recordings, but still present themselves now and then. To test to see if the limitation in midrange detail was due to the K1000 or his amps, we switched to his speakers. All the detail and depth cues were present, though being horn speakers there was a slightly different tonal presentation.
On to bass- the Omega 2 simply has more of it. Far better extension and depth. By depth I mean that you can hear "into" the bass; it has its own space, it sounds real. With the first pressing rock we used, the discs are usually flat transfers (though not always taken from the best tapes) so dynamic range is left intact. I have always been a big fan of his Naim and would probably go as far to say that in a double blind I might not be able to tell the difference between vinyl and CD taken from the same master (where rock music doesn't rely so much on the superior imaging and soundstage of vinyl). Anyway we both agreed the Omega 2 is more seamless in reproducing a drum kit. The K1000 can sound wimpy with kick drums and low bass lines sort of just drop off. Texture on both is fantastic, there isn't much "one note" effect. The Omega 2 even beat out his speakers in bass depth and realism.
With treble- they both extended as far as we could hear. We were hard pressed to find much difference in treble detail. The K1000 can tend to make some cymbal hits a bit splashy, but the O2 does this as well especially on poorly done remasters.
Over all fun time and quite a revealing experience. But the most fun probably came when we switched back to vinyl and cranked his speakers the rest of the evening