IBM x346 and potentially conflicting PCI/-X options?

[eMGeeGFX]

Recently I installed an AMD/ATi Radeon HD5450 PCI (thus not PCIe
or PCI-E as in PCI-Express) card into the low-profile card cage
(providing slots 1 & 2), into slot 1.

Everything seems to work fine, Windows 7 starts up, but everything
is extremely slow, unresponsive and the system usually crashes or
crashes as a result of everything freezing after a while. On top
of that, the cards in the full-sized card cage (providing slots 3
& 4) are apparently disabled.

The contents of both card cages (low-profile and full-sized), are
as described below.

low-profile card cage
- slot 1: Radeon HD5450, PCI
- slot 2: IBM 1000BASE-TX NIC (single-port), PCI-X

full-sized card cage
- slot 3: Neterion XFrame 10GBASE-SR NIC, PCI-X
- slot 4: FireWire IEEE-1394a adapter, PCI


The HD5450 card is the most recent addition and that's when the
problems started. I did disable PCI ROMs and even entire cards,
but the slowness and unresponsiveness would still remain.

Interestingly, when I once disabled the gigabit ethernet NIC (in
PCI slot 2, in the low-profile card cage), one or both (I don't
exactly remember) cards in the full-sized card cage would work
again or be seen/recognized.

Does anyone have an idea what might be going on here? Thanks in
advance.

- MG