I am one of those more than happy LCD2 users with the O2. I have listened for hundreds of hours with the LCD2's R2's with the 2 O2 amps I have and ODAC's and two other amps and 2 other dacs....
The O2 amp is totally inaudible....evidenced by the specs it meets and it totally transparent....garbage in ...garbage out. If you put in compressed source material into the O2 you will get crappy compressed source sound out of it....put in well recorded AND well mastered material into the O2 you will get sound out that comes out very, very well and its amazing at times how good it sounds with this amp. A good amp, like a straight wire with gain just doesn not add or take anything away from the source....
I beg to differ "its all about the numbers" ....if the specs that the O2 were designed against were not met or exceeded it would NOT be a transparent amp. It does deliver the voltage and power to excercise most headphones out there, including the LCD2's...with authority and control.
I would much have an amp that meets or exceeds these specs...than one that does not....we can go from there,
As far as the ac adapter I have tried all of them....and the best AC adapter is the WAU16-400. It is the best transformer for any headphone
The WAU20-200 doesn't result in any higher output into high impedance headphones (because the O2 uses a regulated power supply internally) and it has less current for low impedance loads. The WAU16-400 is the best transformer for any headphone.
The 18 and 20 volt transformers do put more of a thermal "strain" on the O2 as the regulators run hotter.
I can honeslty say that with 4 transformers i have tried and even compared to the pure DC of the batteries I can not detect and real world difference with LCD2's, Q701's or Grado 325is...
Note there is a lot on this subject on the designers blog....take the time to read the stuff on AC adapters and his recommendations.. At first I was not a beliver and bought several AC adapters to see for myself.