Can I just say with respect to the B22; I know it has a lot of supporters here, but I think a lot of the enthusiasm for it may be misplaced.
One of the features of the B22, at least in many incarnations and in its recommended configuration, is a third channel. This is in addition to its existing 'genuine' ground. Operating the amplifier using the 3rd. channel almost certainly degrades the performance with respect to operating it with the genuine ground only. Part of the advertising for the B22 claims the 3rd. channel results in lower output impedance, but this is false. The degradation may be small but for me it throws into doubt AMB's entire design philosophy, to say nothing of his test regime.
Opamps are subjected to extensive test and redevelopment by manufacturers. Their performance exceeds that achievable with discreet designs in most cases. The B22 is overpowered unnecessarily, it is claimed it will drive 18W into 8 ohms. Many people believe that discreet designs are automatically better than integrated designs, but this is not the case. Can you imagine a Pentium processor built with discreet transistors? The only reason for using discreet components nowadays is when power levels beyond those of opamps are required. Such power levels are not required to drive headphones of any reasonable manufacture. Yes, there are many enthusiasts who build discreet opamps and who claim they produce a superior sound, but these claims are not supported by reliable measurements or blind test.
There also seems to be an inbuilt assumption operating that more expensive == better and the O2 is being excused on the basis that it costs much less than the B22.
More expensive == more expensive.
Better == better.
Things that are more expensive very often are better, and very often things are more expensive because it costs more to make them better, but things are not necessarily better because they are more expensive. It is entirely possible to make something that is expensive that actually performs worse than something that is cheaper. It could in fact be the case that, at least in terms of distortion, the B22 performs worse than the O2. Only objective testing, either instrumented or blind listening, can discover the truth. This can be a hard lesson to learn for many people, but teaching it is one of the O2's designer's goals, as I understand it.
Please take aboard some of these ideas before rushing to judgement, or merely expressing your prejudices in this matter.