It's an APCI system.... IRQ's are irrelevant.
This is a 2 year old system...if the sound problem just started, it has nothing to do with the bios.
I gave the link to the correct Realtek drivers in #10....I have no idea why you went on a search and destroy mission for the wrong drivers (not that I think it matters as it pertains to your problem).
Getting rid of the 190.38 drivers is a plus for anyone's system, but it runs off the Northbridge, so I never thought that it was the cause and cure (other than you said it started after their installation).My bigger concern was that 300w PSU you undoubtedly have.That alone could be the 'bacio della morte'.
The PCI card you ordered will be running off the same bridge as the HD chip (as well as LAN, USB and ATA...the 'problem' could be in any of them). Unless the Realtek chip is defective, your chances of encountering the same problem are relatively good. The chances of a defective Realtek chip are close to non-existent. The chances of an under-powered system are as close to obvious as one can get.
That said, my original thoughts were that it was a 'simple' setting (thus my #1 post). At this point, a more likely scenario is electrical interference via the boards VRM's in response to the new card's power pull. The bad news is there's not much you can do about it with the present setup. The good news is the PCI card will likely work..... if it doesn't suck the life out of your PSU.....
....hang on to the receipt.