6.0-RC1 on Promise SX4060 (SETFEATURES FAILURE, READ timed out)

Hi, I am trying to install 6.0-RC1 on a system with a Promise SX4060 
(PDC20621) + 4 Maxtor ATA-133 drives (6E040L0). The mobo is a Tyan 
Thunder LE (S2510).

The card appears to be detected ok :

atapci2: <Promise PDC20621 UDMA100 controller> port 
0xe800-0xe8ff,0xe400-0xe4ff,
0xe000-0xe0ff mem 0xfea00000-0xfeafffff,0xfebd8000-0xfebdffff irq 23 at 
device 3
.0 on pci1
atapci2: rid 0x20 is memory, requested 4
atapci2: Reserved 0x8000 bytes for rid 0x20 type 3 at 0xfebd8000
atapci2: Reserved 0x100000 bytes for rid 0x1c type 3 at 0xfea00000
atapci2: [MPSAFE]
atapci2: DIMM size 1024MB _at_ 0x00000000


but the drive probing fails completely:

ad4 : FAILURE - SET FEATURES TRANSFER MODE timed out.
ad4 : FAILURE - SET FEATURES RCACHE timed out.
ad4 : FAILURE - SET FEATURES WCACHE timed out.
ad4 : FAILURE - SET FEATURES SET_MULTI.
ad4 : FAILURE - READ timed out (LBA = 80293185)
ad4 : FAILURE - READ retrying (0 retries left) LBA = 0
..
ad4 : req = 0xc3b78960 SET FEATURES SET TRANSFER MODE semaphore timeout 
!!DANGER WILL ROBINSON!!
..
..
(hand copied as I don't have a serial console)


These drives seem ok (work with a TX2000 and a 2Ware 7506).

In order to eliminate the drives, I have tried a seagate ST340014A as 
well - same result.

Any suggestions about how to proceed (I would like to get this going)

Cheers

Mark