How to set up 2 hdd in raid0 with ssd boot

That's strange. AHCI is a subset of RAID. So as long as your SSD is not part of the RAID array it automatically defaults to AHCI mode and should be recognized.

Try this:

1.) Connect your SSD to one of the Intel 6Gb/s ports (SATA1 or SATA2) in AHCI mode.
2.) Connect your 2 HDDs to the ASMedia 6Gb/s ports (SATA7 & SATA8) in RAID mode.
3.) Reboot into the ASMedia's RAID BIOS and create a new array.