Finaly managed to get 3 boxes working out of the batch I had and now seem to find the following issues:
Lots of errors like
[2014-06-25 06:49:08] KnC: 3.0.310 Failed to setwork (19)
[2014-06-25 06:49:08] KnC: 3.0.311 Failed to setwork (19)
[2014-06-25 06:49:08] KnC: 3.0.312 Failed to setwork (19)
[2014-06-25 06:49:08] KnC: 3.0.313 Failed to setwork (19)
[2014-06-25 06:49:08] KnC: 3.0.314 Failed to setwork (19)
[2014-06-25 06:49:08] KnC: 3.0.315 Failed to setwork (19)
[2014-06-25 06:49:08] KnC: 3.0.316 Failed to setwork (19)
And hashrate drops to almost 400Ghash when running into a lot of hardware errors.
This "failed to setwork" is caused by the "Advanced window", as soon as you click to another webpage (for instance "Status") the error will disappear... and yes: these errors take about 300 Ghs away from the total of 3.3Th (5 boxes).
actually: you get the best results, by not using the Web-interface at all....
I already emailed KnC, but they have not replied... so maybe someone else (You?) should inform them as well... so they can solve this "failed to setwork" soon.