For TV sources, any will do. If you spend more than minimum, you are wasting money.
You should use HDMI interface between the TV and DVD player. Then use a reasonably priced IC from the DVD to preamp (HDMI carries both the audio & video signals). You will want to take advantage of your plasma TVs video capabilities by utilizing HDMI, even if it means purchasing a new DVD player (if your current player does not have an HDMI interface). Even the most modest-priced newer units have HDMI. Spend more on the HDMI cable than the IC's at the onset. You can upgrade the IC's later
A good HDMI is available from MONO PRICE for $9.95. Better ones are much more expensive so you might want to try this first. I don't agree that any IC will work but you don't have to spend a lot, look at good used ones on Audiogon. If you want to buy new Supra has a good rep. for both and is not too high.
I agree with the HDMI to TV link from DVD. Also placing a pair of ICs from the cable box or DVD (or both) to the preamp is the ticket. Audio Art, and Voodoo Cables make some nice inexpensive interconnects that do a great job. Naturally, more $$$ will get you more there too.
it's redundant to run ICs from the TV back to the preamp... unless you are running an outside antenna setup, and quality will suffer.