I should have said: Each of our PIIX4 IDE ports has the same capabilities as would be exposed through each of the ports on a SATA controller in IDE compatibility mode. 
Although I would think that a SATA controller in IDE compatibility mode would still be limited to (Primary, Secondary) x (Master, Slave), would it not? (I know there are some 8-channel "IDE-ish" controllers out there, but I don't think they are really standard... like four-drive floppy controllers...)
We don't include any guest AHCI drivers. I guess we'd need to provide them on a floppy image like we did for various SCSI drivers etc... But at this stage I believe we do not do so.
Cheers,
--
Darius