Intel ICH6-M failure

hi,

searched quite a few days for a solution and tested different freebsd versions, but still no success.

atapci0_at_pci0:31:2:      class=0x010180 card=0x01871028 chip=0x26538086 rev=0x03 hdr=0x00
    vendor   = 'Intel Corporation'
    device   = '82801FBM ICH6M SATA Controller'
    class    = mass storage
    subclass = ATA

5.4-RELEASE boots without problems while the controller is detected as the following:

atapci0: <GENERIC ATA controller> port 0xbfa0-0xbfaf,0x376,0x170-0x177,0x3f6,0x1f0-0x1f7 irq 17 at device
 31.2 on pci0
ata0: channel #0 on atapci0
ata1: channel #1 on atapci0
...
ad0: 57231MB <HTS726060M9AT00/MH4OA6EA> [116280/16/63] at ata0-master UDMA33

if testing with anything else (5.4-STABLE, 6.0-BETA5, 6.0-RC1, CURRENT) the controller is detected as
<INTEL ICH6 SATA150 controller>.

when mounting the root fs the following error occurs:

ad0: FAILURE - READ_DMA status=51<READY,DSC,ERROR> error=4<ABORTED> LBA=0

found some other threads regarding this failure but upgrading to another version didn't help.
disabling acpi or apic also doesn't have any effect. 
disabling dma, using pio4 didn't work. 

i want to get 6.0 running to be able to use wpa functionality.

any advice?

if this is not enough information just give me a hint.

thx.

torben