If both were brand new, it would have been a more difficult decision.
But when it comes to complex electronics, I would choose the brand new over the used.
I am completely happy with Audyssey Dynamic EQ, and I am not sure if Anthem or other processors have the exact equivalent, which I doubt because every company (Audyssey, Anthem, Yamaha, Pioneer, HK, etc.) has its own variation.
If I were buying a new processor today, I would have to try Anthem to see if they have what I love in Audyssey DEQ and see which I prefer more. But only I could make that determination, not anyone's opinion.
Perhaps you could try both for YOURSELF to see which you PREFER more.