I hardly 'blamed' Gigabyte, I said it was more a 'quirk' of their board.
If (as you say) the SIL3114 supports a single SATA device, why doesn't it on this Gigabyte motherboard (unless it's configured as a RAID5 JBOD array)... because of the way Gigabyte have implemented it.
I'm not the only one that has experienced this frustration (it's not mentioned in the manual or on their website). See this thread (started by me) as an example, it links to other threads that are discussing this 'quirk'.
Anyway, when connected to the NF4 channels the Plextor works perfectly and that's all that counts