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!