I had one that hooked up ATA drives directly to a PCI connector - the Sonnet Tempo HDAre there any nvme or PCI/sata cards that could be used to hook up msata or m.2 SSDs straight to a PCI slot in a power mac? My searches just turn up PCI-express adapters. If there's a good PCI card that does this then it would save a bunch of cables and adapter boards...
For SATA/AHCI/NVMe drives, the only such cards I have seen have PCIe connectors, so won't work. M.2 came out way after PCI became a legacy bus. There is zero market in retrofitting new technology into obsolete hardware so I don't expect any such cards to become available since existing SATA to IDE adapters should cater for the retro crowd.