Had the original "chunky" standard II version but was a little underwhelmed by the sound out of the box, plus it had some issues... some of which may or may not affect the II+
1. the output level is so high it would overload the (digital) pre-amp volume control in my Cyrus 6vs2. Only attenuators really solved this.
2. the usb/driver implementation was by no means bullet-proof, it would pop and click when playing online poker at the same time as listening to music. Not a massive problem but a bit annoying.
3. the device wasn't selectable in music creation software such as cubase, again not a problem to many people but was an issue for me.
All in all a DAC has to be plug-n-play for me, I'm sticking with optical connections. In HRT's defense they were very helpful via email when trying to sort the level problem, I actually spoke to one of the designers which is not something you can expect from the bigger companies.
Another vote here for the II+. I too use it on a Mac which may or may not be a contributing factor of my positive experience with it, but for me it really has been a fit-and-forget experience, and combined with iTunes and BitPerfect, it sounds superb to my ears. I have had no issues with any software which didn't instantly recognise it and use it. I did have intermittent issues with Spotify at one point (sound would sometimes break up and become crackly until I rebooted Spotify) but even this seems to have been solved by either the latest release of Spotify or Mountain Lion (I downloaded both at roughly the same time so I can't say which one fixed it).
As for the output level, it's something like 2.5V peak-to-peak @ 0db, which to be honest a Cyrus amp should not struggle with. If it does, then it's a poor show. I have had CD players in the past which were 2.5V P-P @0db and I had no issues with them playing through what would now be classed as rather elderly amplifiers, some of which even predated CD players. Any modern amp which struggles with the volume output from a HRT II+ should take a good look at itself imo!