I have same problem, just tried to get the 7th card running, still without success. Using also the MSi-Z87-G45 board. Will post here if I find a solution on the way to RiCHDoM

2 question I have please:

1 - When will I be able to use my 750Ti to ride Hiro? To bad if I would have to mine something else with it  
                                                                .
2 - Is a WU of 0.030/m good/average/bad/wtf? with phfsgminer (using 280x)

Thanks!
IM