Yeah that's the fun part of this hobby for me I guess...the variety and subjective part and perception of each individual when it comes to sound/equipment preferences.....it will be boring if everyone's view/choices/opinions is the same.... and if I was being objective than I would have to say that the O2 and C5 or in fact many well built amps would actually sound the same.(Ok I might get flaked for this statement but...)
I remember sometime back there is actually this amp challenge that you could try and win 10,000 dollars by trying to identify the sound diffenrence in two amps...any two amps if I'm not wrong, though I'm not too sure if you could still try it now and if I'm not wrong nobody has yet to win it.
Let me see if I could find the faq link to it.......ok below is it.
I personally believe that and also that it has been proven scientifically with blind testing. Not to say every amp sounds the same, but that some are indistinguishable from one another but people will still think they hear a difference.