This is a long post.  But here goes.....
To start with; this is my current setup:
FRONTS: Paradigm Studio 100 v3 [44-22kHz +/-2dB @ 91dB]
CENTER: Paradigm Studio CC570 v3 [60-22kHz +/-2dB @ 91dB]
SURROUNDS: Paradigm Studio ADP470 v3 [90-22kHz +/-2dB @ 91dB]
SUB: Paradigm PW-2100 (ported)
1) I feel my current sub is somewhat lacking.  It is okay for movies.  But when I listen to CD's it sounds awful.  Too boomy.  Not very clean.  I guess this is what people mean when they say the sub is either suited for movie only or music and movie.  Currently, I prefer to set my fronts to large and listening to my CD's in 2 channel stereo.  Then the bass has more punch.  Sounds more natural.
2) For starters what are the advantages/disadvantages between a sealed and a ported sub?  Or should I not consider this when buying a subwoofer?
3) Is there a ration between sub and speaker cost that one typically uses when trying to find a sub?  
4) One possibility is going up to the Paradigm Servo-15.  Is going to a 15" sub too big when compared to the 6" woofers on the Paradigm towers?  Or is that not a concern?
5) I am staying away from HSU and SVS for now.  I do not like mail order.  I prefer to listen before I buy.  That leaves my only other choice with Velodyne.  [If I can find a place that sells them.  Future Shop only sells the low end Velodyne’s.]  Would the Velodyne DD-15 be the closest match to the Servo-15?  What do people think about the DD-15?  I noticed that it comes will all these DSPs (Jazz, Pop, etc).  Do you have to use them?  I personally think it's a gimmick and prefer not to have them.
6) Just found out that I could get a JL Audio S13 for $5000.  Apparently it's a really good sub.  

  But a little expensive.  Hmm, I must have heard him wrong.  I can't find an S13 on the JL webpage.
7) Okay, this new sub will also have to be able to integrate with my other towers: Klipsch RF-35 (37-20kHz +/-3dB @ 98dB/2.83V/m, 8ohm) and Yamaha NS-8X (35-50kHz @ 92dB/2.83V/m, 6ohm).  Does anyone see a problem with that?  Or would the PW-2100 be a better match for any of these?
8) Last, I am still having a hard time with the cross-over setting.  Since the ADP470 only go down to 90, should I set to x-over to 100Hz?  Does it matter?  Will I damage the speakers if I send it lower frequencies than it's rated at?   PS: Sometimes I listen to 7 channel stereo.  So, the surrounds don't just get used for movies.  I'd prefer to use 80Hz.
PS: What is with the new ADP590's frequency response of 85-10kHz.  I guess they don't require to reproduce the highs anymore.
Thanks a lot.  Hope to hear from you soon.