I am eagerly awaiting my first U2. These responses will be of great assistance when I throw it in with my U1's and Bfgminer running on a Raspberry Pi system. I had all the same problems trying to get my U1's to work. Two things made a huge difference.
1. Purchased a large 5vdc switching power supply to run my USB hubs... allowing almost 1 amp capacity for each miner.
2. copied the following statements in the following order to my bfg commandline:
     --set-device antminer:clock=x0781  --icarus-options 115200:2:2   --icarus-timing long -S all

The icarus timing long statement causes the clock and hashrate to continually correct itself and is not appropriate in computer systems with a cpu load shared with other applications. You could experiment with "--icarus-timing short" which requires full CPU time without delays, and makes the self-corrections,  but only for a limited time (~1 hr). Observing this, I saw my hash rate jump all over the place but over the course of a couple days it smoothed out until now after a couple weeks of continuous running, I see 3.16 or 3.17 gh/s on each miner with total errors at 0% and total rejected at .08% Very pleasing.