PI board? Backing up between PCs? Graphics cards?
I don't know what the first thing is but it seems to me you have 3 completely different questions.
The graphics is relatively easy but you don't say what you want to use it for, whether you have AGP or PCI Express and how much you wish to spend. Or any details of your PC either. A direct replacement for your card AGP and cheap with DVI output click here its virtually the same card as you have already just with a DVI output.
I have to say that personally I see little point in changing a graphics card just to get the DVI output as its better admitadly but not that much better.
Regarding the sound, its not combined and I think you are a bit confused here. You have 2 seperate items, a graphics card and a sound card. Either of them might be onboard and they work together but they are seperate.
Sorry but you posting is rather confusing and I think you should clarify what you have, what you want to do and what you can spend.