I have a buddy that broke off one of his onboard Sata Connections trying to add two more hard drives on an Asus P5k-e Wi-FI motherboard. my first though was to pick up some E-sata to Sata adapters (fleabay under 10 bucks)
Down and dirty
PCI raid card that support JBOD Vs PCIe (this board has na open Pcie x4 slot) vs replacing the motherboard
The E-sata adapters are under 10 bucks
the PCI card is under 40 bucks
the PCie card is also under 40 bucks
Replacing the board means re-installing everything and I would be doing the work he doesn't feel up to it.
Installing a PCI or PCiE card shouldn't disable anything in the bios
I would assume with only SATA 2 hard drives both PCI and PCIe should have the bandwidth to keep up.