I'm glad you bought them
They're one of those headphones that really won't do you any wrong.
In regards to your questions:
1) Mojo pairs phenomenally with the HE-560. It has enough juice to drive it to adequate volumes. Heck, the Mojo also sounds good with the HD800s. Must be some sort of magic Chord worked.
The Mojo is detailed, relatively neutral, and certainly serves as an excellent solution (portable as well) to driving the HE-560 in the office or even at home.
2) I'm not a stickler for perfect DSD/DXD files. I'll admit I listen to as many 320kpbs files as the next person. The HE-560 sounds great even out of my Sansa Clip + if you can believe it (Max volume)
My music preferences range from electronica, alternative, rock, r&b, hip hop, to classical. So yes, I do listen to "modern" music.
Lastly, I definitely don't think the HE-560 is sterile. Even on extremely flat/neutral sources, I found the HE-560 to be very enjoyable. They definitely are airy and detailed enough. Soundstage isn't massive, but a clear improvement over the HE400i.
Wish you the best of luck! I'll think you'll fall in love with them. Just don't be like me and purchase the HE-1000 later on