As an idea, with 6 U1's you should be using a 12V powered USB hub with at least 3A rating, preferably 4A or more. I use Raspberry Pi Model B plugged into a Orico 10 port USB 2.0 powered hub rated at 12V & 4A, I currently have 7 U1's plugged in and a Arctic Breeze USB fan and get a steady 2.0 - 2.1 on all miners. These U1's run pretty hot even on low clock, on high they get too hot too touch unless you have add some cooling, this slows them down. With my fan cooling them they barely even get warm to the touch.
To "fine tune" Bfgminer for the U1's and maximise your return from the pool you could also run it with the "--no-submit-stale" and "--icarus-options 115200:2:2" parameters or add them to your .conf file.
It would also help if you pasted your .conf file (without any info you don't want posted), or perhaps you can make use of mine below. Although you can ignore most of it since I am using api options to work with my Adafruit I2C LCD screen. The most important ones for you are the last 4.
As an example, my .conf file which I use for Slush's Pool is as follows:
"pools" : [
{
"url" : "stratum.bitcoin.cz:3333",
"user" : "User.worker1",
"pass" : "pass"
}
]
,
"api-listen" : true,
"api-mcast-port" : "4028",
"api-network" : true,
"api-port" : "4028",
"api-allow" : "0/0",
"expiry" : "120",
"failover-only" : true,
"log" : "5",
"queue" : "3",
"scan-time" : "60",
"worktime" : true,
"shares" : "0",
"kernel-path" : "/usr/local/bin",
"scan" : "antminer:all",
"set-device" : "antminer:clock=x0981",
"no-submit-stale" : true,
"icarus-options" : "115200:2:2"
}
I use the 0981 clock speed, 0A81 gives me faster hashing rate but as much as 40% errors so is counterproductive. With the above setup I get literally 0 hashing errors even after many days which I was surprised by.
Hope this helps
Oli.