Bringing up new Intel non-legacy system

Although I'm a network guy, for various reasons I am helping to get
FreeBSD running on a new Intel system: S7000FC4UR. This is a
rack-mount server that has no PS/2 or PCI legacy, its all PCI-E
expansion, and only USB peripheral. I have had a lot of issues:

First, the DVD is SATA, however I can work around that by setting
IDE mode in the BIOS.

With FreeBSD 7 BETA the install kernel always seems to hang
in USB initialization, if I disable ACPI it gets further, but ultimately
still no joy.

Oddly enough, STABLE OCT snapshot will actually install  but
again only with ACPI disabled.

Anyone have an idea why 6.X would actually faire better than 7,
this surprised me?!

And, is the ACPI subsystem likely to be the source of the problem?

I would really prefer 7 running on this, and of course with ACPI
working.

Oh, the system also has LSI MegaRaid SAS 1078, which I was
able to install using STABLE.

Cheers,

Jack