I was mainly making sure you weren't picking a set of THX computer speakers.
Also your German links aren't accessible here in the US. Jamo here is "about dead". (it would help to include your location)
Never heard of Teufel.
But to answer your question, no you do not "need" a THX AVR. Besides, Onkyo/Integra is about the only company that cares to get certified anyway. "Over there" may be a different story with Cambridge...but we don't have Cambridge here.
I'm an ex Brit soldier living in Germany. Jamo are making waves here with THX 5.1 systems and Teufel are a direct supplier German make like Salk in the US.