Hi guys, been a while since I've been on here, the last time I was I had such great advice from individuals I did not need to frequent but tis the time to upgrade and looking for advice again. I believe the last gentlemen's name that helped me out was RobertJ if he still lurks on this site. Anyways, I'm currently running a Harmon Kardon AVR247 (not now but will be upgraded later) with a Behringer EP1500 into a Exodus Tempest X2 15" sub in a 5.1 cubic foot enclosure tuned to 21hz and couldn't be happier. This sub/amp combo has been amazing and I know the Exodus is no longer available so I'm basically looking to add a second sub and know I will need more power. I was thinking of either going with the Behringer NX3000 or Behringer EP4000 to double the power, the EP4000 might be a bit much for the Exodus being a 1000watt sub and running 2000watts into it if I'm reading specs correct so maybe the NX3000 will better suit me. But what subwoofer could I use that would be comparable?? I was thinking of going with maybe a Sundown SA15 or maybe a X15 or maybe even go with an 18"? I'm not interested in $800 subs, I'd like to keep it between $300 and $500. Thoughts, comments, criticism, suggestions please! Thanks in advance.