New External HDD Shows As SCSI in Dev. Mngr. IDE in BIOS

[Ex_Brit]

First of all the BIOS is set to AHCI.
All drivers are up to date and yes I've tried uninstalling controller drivers, the drive itself to no avail.
It's a 3TB LaCie eSata GPT volume (so Windows would accept an over-2TB drive), formatted NTFS (4 partitions).
It replaces a LaCie 1TB one which suddenly conked out - which was connected in exactly the same manner and showed OK as an ATA drive and as an HDD in the BIOS.
Furthermore that ATA Channel is now running at "Ultra DMA Mode 0" as distinct from Ultra DMA 6 with the old drive. Also the drive shows now as SATA I during the boot, before it was showing SATA II
I set AHCI recently with the OS already in place, so that may be a partial cause.
Any ideas to remedy this situation, or isn't it dire? I did some searching and found similar threads which I'm afraid didn't answer anything.
(See my system details & attached pic for more info).

 

[Ex_Brit]

Further investigation and exhaustive online research show that, under Storage Controllers, the Marvell 91xx SATA 6G Controller is to blame.
I have now set Windows to never install driver updates from WU automatically.
It's uninstalled and now during boot my external drive shows as SATA I - incorrectly (should be SATA II) but at least it's recognised..
It's now taken care of through an extra item under IDE/ATA/ATAPI controllers as in pic below.
But I can't seem to improve on transfer speeds in those 2 ATA Channels that alternate between Multi-Word DMA and Ultra DMA 0.
That stumps me and am wondering if I should perhaps scrap AHCI and return to IDE.