Macintosh bootable volumes are supported on the internal 2-port PCI card (part number TSATA) but are not supported on any of the other SATA cards at this time.
After Apple released Apple Mac Pro EFI Firmware v1.3 on 3/27/08, the Sonnet Tempo SATA E2P card no longer worked in slot 2 of the Mac Pro Early 2008 Model 3,1. Slot 2 is a x16 PCIe 2.0 slot. The solution is to move the Tempo SATA E2P card to either slot 3 or 4, which are x4 PCIe 1.1 slots. The Tempo SATA E2P card works fine in the PCIe 2.0 slots in the Mac Pro (Early 2009) Model 4,1.