[Sussex] Whats the difference?

[John D.]

Amongst other things, I've been dreaming about the possibility of 
getting a barebones system and then customising some of the components.

As far as I can see, most of the barebones systems available are pretty 
garbage i.e. trendy cube models which seem to lack expansion.

Ideally, lots of pci slots would enable me to "play" to my hearts 
content, but now the buggers seems to be changing the ball game (again).

I see that the latest standards of graphic card interface is PCI-x(16x), 
but I also have read reference to  "normal"  PCI-x slots and  PCI spdif 
out slots

Whats the difference between the latter and are they compatible in anyway?

regards

John D.