The magnum is an extremely musical sub. Supposedly the new ones will get extremely low and loud all day long. I had a D2 spoke basket (2nd gen) and by far the best woofer i have owned.
I have heard great things about the IDMAX, i have one sitting on the floor in my room waiting to be reconed . I'm sure you won't go wrong with either. I'd personally pick a new magnum but they are about $100 more than an IDMAX