Another thing to consider is for dbl the volumn level take double the wattage. That said, with your X4000 you would run out pretty fast. I am told these are great if you have a high power amp. ADA 1250 or Emotiva AXP2 etc.
These HP Speakers will probably suck the power supply in the Denon dry pretty fast.
I don't understand how loud you really need to play, I have a HK 3490 now and M80's I sit in a room 20 x 13 x 8 and Speakers are set 11 ft apart I sit 13 ft away and if I get to +5 I sure as heck can feel air movement and I only got two Energy 10ESW subs. This reciever is a 2ch 165w per, I couldn't even phathom a 450 w power amp at loud volumn unless it was outdoors