I've had the O2 paired with my DX100 for a few days, and it's indeed a great combination. I've had some suggestions to try the Tralucent T1 amp as well as the iFi iCAN amplifier. The iCAN has a unique "3D" switch that sounds intriguing; I'm a sucker for a deep, wide soundstage. However, I really like the O2's footprint along with it's ability to power the LCD-2 effortlessly; it fits neatly beneath the DX100 with a very short IC cable and makes a great transportable package.
I'm still getting used to the quirks of the DX100, so bear with me... why does the unit only display some album art and not others? All the graphics are named "folder.jpg" but only about 1/3 of them will show when I play music from their respective album folders. I have tried resetting the DX100 multiple times, and have let the device sit for long stretches after rebooting before touching any controls (in case it's still sorting and indexing). Do I need to reformat the micro SD, load all the music again, and start fresh? The very first time I booted the player after putting music on the card I may not have let the indexing proceed long enough.
BTW, I currently have a mixture of FLAC and WAV, mostly 44.1/16 but some high res files also. The firmware is 1.2.7.