As an update, I found out that the ROCKPro64 seems to be working with LSI HBA controller cards: https://forum.pine64.org/showthread.php?tid=6763
And such controllers with 16 ports can be found on eBay (with P20 firmware IT mode, meaning no RAID and no BIOS) for about 45€: https://www.ebay.fr/itm/LSI-9201-16e-6Gb...3291384883 for example.
With 4x SF-8088 to SATA at 37€: https://www.ebay.fr/itm/4pcs-Mini-SAS-26...2683726119
Total 82€ for the controller and SATA cables.
Only question I have is, how does it works when you only have x4 PCI-E and the card has x8 PCI-E?
And such controllers with 16 ports can be found on eBay (with P20 firmware IT mode, meaning no RAID and no BIOS) for about 45€: https://www.ebay.fr/itm/LSI-9201-16e-6Gb...3291384883 for example.
With 4x SF-8088 to SATA at 37€: https://www.ebay.fr/itm/4pcs-Mini-SAS-26...2683726119
Total 82€ for the controller and SATA cables.
Only question I have is, how does it works when you only have x4 PCI-E and the card has x8 PCI-E?