Hi Ben,
You need the OS2AHCI driver to actually support AHCI controller. The regular DANIS506 driver will only work in IDE mode, meaning: it'll support the normal PATA and SATA devices only.
Are you running the AHCI driver already?
If yes, than the only thing you can do is log a request with the AOS folks to support the NVidia hardware, but given the age of that chipset I would think that is very unlikely to happen. Still, worth a try...
In case you are NOT using the AHCI driver and want to simply use the DANI driver, the approach you can take it so shut off AHCI in BIOS and simply have the controller come up in IDE mode. Most motherboard configurations that support AHCI have this control, at least the ones I have seen first-hand.