For the cards, iem is to be avoided, sounded bad with SE5 to my ears, with sort of sibilant raspy mids. Balanced is good and discrete is more neutral. Never tried Minibox.
Never listened to DX9O.
Didn't realize it til reading this thread but, for some reason, I only use the physical volume buttons on my r10 (guess I prefer gradual volume adjustment that NO slider I've ever used can provide).
UI is a bit different on the r10 vs dx100 but (from pics an videos I've seen) onscreen volume slider appears same. I do recall reading in one of the threads here (sorry, not sure if it was the r10 or dx100 thread) that power output may have been a bit reduced on the r10 to help increase batt life. So it may not have exact same max volume as dx100 but all reviews I've read on both still say they can drive difficult headphones.
Never maxed my r10s vol yet (not willing to test this theory; may change when I finally buy some hungrier phones) but I don't doubt it could have similar issues if not careful with onscreen slider.