no problem at all using an extension cord. they pull almost no power at all.
however, you should have the tv and all the components on a power strip with surge protection anyway. that would be my purchase if i was gonna add a cord. a decent surge protector is worth it's weight in gold if it has to do it's job. saved my arse a few times over the years. you don't need a $90 one but a good $15 or so on one won't break the bank.