My Prisma has never gotten more than 350GH/s. My opinion is that they are pieces of shit and should not be purchased. I can't even return this piece of shit because my reseller (Canary) basically blamed me and told me to fuck off even though it arrived with missing parts. Be warned if you buy one of these. You will waste more of your time then they're worth and will be disappointed.
That doesn't sound like Canary. You must have really pissed him off.
Did you make sure the boards were chained in incremental order? (Example: 01:17,02:18,03:19,04:20,05:21...) I understand it is crucial.