DR-680mkii = lipstick on a pig
You're the unlucky one who had 2 or 3 units malfunction, right?
The <<lipstick pig>> might not be so bad though, bot only If they keep the street price at the current level (as low as 400$).
The truth is that, according to their own statements, they only really upgraded 3 things:
Improved audio quality - probably similar to Busman mod - and they also fixed the underspecified capacitors for phantom power. I wonder if they chose the same op-amp as Busman? That would be funny.
SDXC support, along with the <<readily available>> SD and SDHC cards probably means we won't see an updated supported media list, which could also translate to better reliability and less problems with lost recordings, especially coupled with the next upgrade
Improved battery life - which, among other things, translates to a new power supply design that could fix many of the problems they had with overheating units, freezing units, power issues leading to lost recordings and 0 KB files.
Another three upgrades are firmware related and could have easily been added to the mkI:
Dual level recording - the only real software upgrade
Reset file take no. (really? This shouldn't even be mentioned as an improvement, it was supposed to be there in the first place)
Playback of multitrack files (the same, it should have been there from the start, especially considering that mkI wouldn't even play back its own recordings once copied to the PC and back to SD again)
Another one is a faux point:
lithium battery support - lithium AA's work everywhere - and they cost 20$ for an 8-pack. Who wants to pay 20$ for a one-time usage?!
And finally there's the
'internal clock oscillator' improvement which nobody even complained about afaik.