Well, as trossman kinda said, every tuner can only catch 1 signal at a time! So multiple tuners are the only way to go, I fear...
I don't know how this works with DVB tuner cards, though, they can also catch only 1 channel at a time, I believe, but how does it work? DVB, as the name says so itself, is a broadcast and, since it's digital, why does it need to "tune" to anything? Isn't all the data there already? Shouldn't that be able to watch more channels at once?
I believe set top boxes are pure evil, you have no control over *anything* whatsoever! They're the only kind you can find in backwater Belgium, though. Every digital tv provider makes you use their box (except TV Vlaanderen, but it's a satellite provider, and I don't want to put a dish in my bakyard.)