you need to tell it to use a different clock speed, the default is not overclocked and can be lower than the 1.6GHash/sec when you start BFGMiner
bfgminer -S antminer:all -S erupter:all --set-device antminer:clock=x0981
the -S antminer:all just tells it to look for them and use all it sees, same with the erupter ( if you ever get more, sometimes others show as them too )
the --set-device antminer:clock=x0981 tells it what speed to set the AntMiner U1 ( or U2 if you ever get one ) and this is the highest setting with out soldering on resistors ( and stable ) getting you close to 2.0 GHash/sec.
You will want to invest in a powered USB hub that can deliver more than 500 mA @ 5V per USB connection. Most motherboard connections can actually do close to 2 Amps ( not all can, check the fine print in your motherboard manual ) when you use a front pannel connector TO the connector on the motherboards. It is a keyed 10 pin ( actually 9, one pin missing on purpose to orient it ) and I've used it for connecting 1 Ant and 1 Erupter with no power issues.
Good luck.
