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I just did some subjective tests using Daft Punk's "Voyager" song (16/44.1 EAC CD-ripped) with the M-100's.
1.0x gain:
- source volume ~ 50% of max
- O2 potentiometer ~ 8:45 position
- volume is louder than I would normally listen to music at
- no background hiss
2.5x gain:
- O2 potentiometer left at ~ 8:45 position
- source volume left at ~ 50% of max
- no background hiss (strange, I could have sworn I heard the background hiss earlier.....stopping the music and turning the potentiometer, I can start hearing the background hiss at around the 12:15 position [I did this after doing finishing the testing session])
- volume is much louder than I would normally listen to music at, so I adjusted the source volume until the volume at 2.5x gain is about the same as 1.0x gain (rough estimate): now source is ~31.25% of max (yeah yeah this isn't objective having the by-ear volume guessing)
- I don't notice any degradation of the signal with the lower source volume
So with the 2.5x gain at a lower source volume, I might be losing bits, but I can't hear it, at least not with the M-100. Having the potentiometer at the 8:45 position is pretty much the bare minimal "angle" before the channel imbalance kicks in for me. So even with the ~50% source volume at 1.0x gain, I have practically no wiggle room for volume adjustment using the O2.
i thank you ever so kindly =]
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The easiest way to explain "why high impedance headphones" will be quoting Beyerdynamic FAQ page:
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edit: re advantage of high-impedance headphones
Aside from weight of the wiring driver coil, yes, higher impedance means that a certain noise level will transfer less power to the headphones. Likewise, if the sensitivity is lower, a given power level will create lower sound pressure levels to the ear. Often times, increasing volume does not scale up the noise as much as it does the signal. So for higher-impedance and less-sensitive headphones, if you're compensating for lower volume by boosting the signal levels (to listen at equivalent volume as another headphone), there will likely be less noise than for normal listening with another headphone. You get higher SNR.
This is why you could say that sensitive IEMs have some of the most exacting requirements for audio systems. They'll pick up very low noise levels. This is one of the reasons why relatively-noisy tube amps are not disasters with high-impedance fullsize headphones—in fact, many people like the combination.
In practice, unless you go to the extremes, like sensitive IEMs, noise is probably not an issue.
thank you both very much
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The real end of the road lies at a live concert and a good cold beer....
lol
Alex
you inspired me to get up and fetch a beer
as for the O2 being the end of the road, excluding electrostatics, i can easily believe it (and i say "believe" rather than "agree" because im not nearly informed enough to make such a claim). "wire with gain" is exactly what im looking for, and in this thread, i imagine everyone else is aswell. however, other things are to be considered when choosing an amp, such as channel imbalance, which is in my very humble opinion, the only issue with the O2, though im confident that once iv changed my gain options, and start using unity gain, this will no longer be an issue at all (due to the more-to-the-right position that unity gain will require).
HOWEVER, marketing schemes and such are pretty powerful, and for the life of me, i cant imagine staying with the O2 when i eventually have enough money for real TOTL gear, and im sure that ill get atleast an asgard, knowing full well that i dont actually need it. kinda ashamed of admitting it, but i never lie.
unrelated question: why cant i power headphones with the odac? i can control its volume digitally, why not use it for sensitive, efficient headphones? ive never tried it due to the massive warning jds labs has printed on the instruction manual that comes with the odac (yes i read it, for me its part of the fun of getting new stuff - being geeky about it
). will it "underpower" the headphones? will it damage them? will it damage the odac?
I was just worried if I've missed something. Feels good so I think I'll pass playing with DIY stuff for now. 
