I think I have found a card that just works:
The two I had to return to Amazon were:
LSI SAS 9207-8i KIT 8-Port 6Gbps SATA+SAS PCI-E 3.0 HBA Kit - same as the Chinese one but £150 and very flakey.
StarTech.com 8 Port SATA PCIe Card - £100, just couldn't manage 8 x drives.
Highly recommended.