Best subwoofer for Linn AV system

I've been reluctant to buy a sub, living in a condo.......but the upgrade bug is going strong and I'm considering buying one.

My system consists of Linn AV5103 pre/pro, 5xAV5105 amps (soon to be activ for the front) which consists of AV 5140's and an AV 5120 center, Snell K.5 surrounds. I'm inclined to go with the Linn sub (AV 5150), but it is $5000.... I'm wondering what experience others with similar systems have had with other subs and how it's worked out.

Any help would be greatly appreciated!!
Don't think you'll do significantly better than Linn's own sub (expensive as it may's designed to work with the Linn's). The old axium..."if it ain't broke, don't fix it". or..."if the team works together, don't change the line up!"...and there you are.
I too have the 5140's and 5120's. I tried the Linn sub. It just would'nt play loud enough. I ended up with a Velodyne HGS-18. It out performed two Linn subs at a fraction of the cost.
Hey Curt, I've considered an HGS 15, or possibly an 18, just how loud do you play your system?? Do you think the HGS 18 is needed, or is the 15 enough??

What kind of difficulty did you have integrating it into your system?
In your setup I'd use the HGS-15. It's not that I play so loud but my listening area is huge. No integration problem at all. I crossed over all the Linn's at 80 hz. When the 5140's don't have to do the deep bass they are much more dynamic. Trust your ears though, a lot of audiophiles don't like deep bass and the Velodynes go deep and clean.
I would highly recommend the AV5150. I have aktive keltiks as my front channel aktive 5120 as center and aktive kabers for the rear and the 5150 is great for both music and movies. It blends in with the system seamlessly. For a less expensive option Linn now makes one they call the Sizmik, I have no experience with it though.
See my thread under "Linn AV4140 feedback?"and also "HT subwoofers"
I personally do not think that there is a problem with the AV5150 subs ability to play loudly(if it is set correctly... crossover/positioning relative to the listening room)although I am about to add a second one (BIG room)
But my strongest recommendation is to listen to everyones opinion,listen to all subs available to you and then make YOUR own decision...let us know how you get on
Marc774, I have two as well in a very large room (w19'x L34' x h12'). I added the second not to add volume but to tighten up the lower frequencies, which worked wonderfully. I agree - set up and room positioning is critical to performance.
It is amazing how GOOD musical bass can be miss-understood for LOUD(30-35htz hump) bass.I did not mean to imply that loudness was my reason for consideration of a second sub.Kevin M my room is not as large as yours at 32'lx8'hx15'w(but I unfortunatly do not have the keltics)so when I get to borrow a second I am sure I will be £3100 lighter
Marc774, well said -- the goal should be for accurate (musical) bass. You should find a noticeable improvement with a second 5150. E-mail me if you would like suggestions on placement, I can provide you with what worked for me.