The added drives will only be operated at U80 speeds, as that is the maximum speed of the PERC2QC RAID card.
You did not state which interface card is in the PV200S. If you have SMM's then there needs to be a terminator card or physical terminator on the SMM in the other slot.
Also you could well be dealing with a cable problem. Look at your Array Manager logs to see if there are any SCSI sense key=0B, code=47 logged errors that would indicate a cable or termination issue.