It seems that the USB is really poor soldered, but till now nothing broke. I am getting about 380GH with 8 boards .... Next thing is that somehow boards are stopping regulary (nearly every 5-10h) & can`t find the solution till now - on some starts there are massive USB errors what end in an crash of cgminer.
I noticed the bad soldering quality as well, as I've mentioned earlier. Not good for a 700 euro product - also the hashrate is far from promised. My stack of 4 boards has luckily been stable once I've got it running. Might help that I'm feeding it cool air to begin with (~5 deg C), so board temps are sub-50. If you get USB errors on starting, turn off power for the whole stack for 10 seconds, then power them back on. That gets mine running after the USB errors.
What`s again (not) funny that the settings for 8 boards are not working - you will need the settings for 4 boards & cgminer will recognize boards correct.... but far away from the promised hashrate. When using settings for 8 - same USB errors are coming up as happening on some fresh starts of raspberry pi & 8x bitburner fury connected via CAN bus cable.
Sometimes it happens that from the full stack only the single board that is connected by USB starts hashing, and the rest of the boards don't do a thing, even though the yellow comms led blinks every now and then. I have to power cycle the whole stack when that happens. Looks like firmware error - maybe the "controlling" board doesn't detect the rest on CAN bus correctly or something.