Pros: Clear sound across the FR, portable(ish - size but battery), drives both IEMs and full size can well. Low noise floor
Cons: you may want RCA-ins when you get it(I did).but portable :D ! Australian wall wart, 2RCA-3.5mm plug and 3.5mm to 3.5mm short interconnects would be g
The volume pot tracking is not very smooth (catches a bit on some positions (tactile feel, not audibly)). (will check whether pot knob gets caught on the case) (edit: yep, that's it, no real quality issue there)
To my surprise, the unit does not come with a 2RCA->3.5mm or 3.5mm to 3.5mm .I only had a fairly long and rigid one. I wish Oliver would include at least some cheap interconnects
I'd probably also like a small manual explaining what not to do. (e.g. will it explode if I leave it plugged in for a weekend at work, and come back on mon to find my building charred. Or does the charging circuit cut off at a certain voltage? does it get powered from AC or via batter when AC is plugged in?), or is pressing the gain button while the unit is on bad or not, etc. How to change the NIMH batteries or something. (and rules of when to charge them for longer life or something. What warranty do we get? What are the return conditions for the warranty claims (who pays shipping where), etc)
I also wish Oliver could source Australian wall warts, but he couldn't at the time. The AC-AC 15v 0.5A adapter with the UK plug is huge. I could only find replacements w the AU plug at Jaycar and Mwave, and they're $30+ shipping ($50...). To be fair, he did give me an option of a small partial refund and me finding my own PSU, but it's probably best to just use the UK one with a socket adapter
That aside, I've been playing with it for a week now, and the sound is great.
Crips,extended bass and highs, present mids, great perceived soundstage and dynamics.
The low output impedance and the decent max output let me drive my GMP 450 PRO (300ohm, no idea what sensitivity. Sound great at hi-gain/about 3/5 of the vol) and UM Mage (demo)/Shure se425.
Both the IEMs and full size cans sound a lot better than my Musiland MD11 and MD30 - much lower noise floor and perceived sound clarity, fr linearity and bass quality (tales of folksy better extension and depth go here). I did expect that for the IEMs, since the hp jack on MD11 and 30 is 2-3ohms, but certainly didn't expect that much of a difference for GMP450 PRO. I'm also rather surprised, just how much of a difference a low impedance output makes for IEMs.
For IEMs, O2 also sounds noticeably better than my Cowon d2 portable. (hmph, I might have to start carrying it around )
The build/case all look and feel very sturdy.
Despite the designer's comparisons to Benchmark DAC, I did not find the sound to be similar (I thought DAC1 was awfully bright, almost serrating, which was not the case with the O2). edit: there is a slight qualification to this, MD11 has slightly rolled off HF as per the RMMA, so YMMV on this a bit, but I don't expect it to become awfully bright on straight (+-0.1db) FR sources.
I wish I bought a desktop version (6.5mm out, 2RCA in) and a portable version , but Oliver/EA and NwAvGuy did very well.
PS I will be cracking it open next week at home and maybe posting some pics on what's inside (part quality and all, not that NwAvGuy approves ), tho I'm not sure if there's any point, since the O2 thread probably has some