This is my first review submission for head-fi, hope that it could provide some comparison and enough information to let you decide whether to make a buy for it. But do remember this review is from my point of view and the ultimate decision is down to your ears to decide.   Tips for mods and results of modding are listed at the bottom of the page. Do note that modding the O2 is done at your own risk, Don't hold me accountable and say you've blown your capacitors because opamp is inserted wrongly or the rating does not match.   PS: My O2 is 4-5...