how are these subwoofers in terms of SQ/SPL i know that focal is more of a SQ speaker rather than SPL but i was wondering how 2 of these would sound with about 500 watts running to each sub. Also, what kind of box would you put these in? Ported or Sealed One more thing, what kind of amp would you run to power these I was looking at the PG Xenon 1200.1, or the RE 12.1, if you have any other reccomendations let me know Thanks in advance!