Morning person 
My sub is a Kliptch RW- 12D.
It does not sound right with DVD music concerts.
Kind of a constant Brrrmmmm sound under the music like it cant keep up.
I believe it will be going back. I tried to go cheap and it sounds cheap.
Or maybe I am not a sub guy!
One thing that I think should be discussed is what your goals and expectations are with a sub. The reason that I am bringing this up is I am not sure of how much more bass you want. I used a Radio Shack sound meter with a correction chart from Rives Audio to measure my room. The Radio Shack meter is "off' at low frequencies and the correction chart allows you to get a reasonably accurate picture of your low bass response. My LS360s measure flat at 20hz and up 3db at 25hz in my room. That's pretty impressive performance for a pair of speakers. What a sub can give you is even lower output and more output at higher db. To be honest, it will take either a really powerful single sub or two powerful subs to add any meaningful impact with already exc. output of the LS360s. Movies hit really loud dynamic bass peaks however. A good sub or two can add impact. For music, I don't bother with my subs. I'd suggest either you buy a test bass cd or download and burn the test tones off of the Real Traps website. Use those with a Radio Shack analog sound meter if you have one or can get one to see what's actually going on in the room.
Further, you should consider equalizing any sub. The easy way to do it is to buy a Velodyne SMS-1. There are many advantages to crossing your speakers over to a sub and using an eq. First, most rooms have powerful room modes. For example you could have and be unaware of a 15db peak at say 33hz. The effect ot this is that softer more delicate sounds can be masked by such huge bass peaks. The bass is drowning out the mids and highs to some extent. Another reason is that removing some of the strong bass from the LS360 can reduce intermodulation distortion, per Ron-C. Also, equalizing the sub allows you to more efficiently use the amplifier power. By reducing the level of the room modes which are just drowning out the rest of the frequency anyway, you leave more amp power for the places where you really need it in the subwoofers output.
Although the easy way to do it is just use a Velodyne SMS-1. I prefer to uses a parametric EQ. The one that I have used for years is the Rane PE17. The Velodyne measures at certain frequecies that are commonly a problem but does not allow for as fine of an adjustment as a parametric eq. For example you could have a room mode, bass peak, at say 39hz and not 33hz where the Velodyne may measure. I forget exactly the points it measures. So you can more precisely reduce the bass peaks with something like the Rane model. For most folks, though, the Velodyne will offer a huge improvement and be all that they need.
The other factors are speaker placement and seating location. If you ever do measure your room, you will likely find that different locations measure quite differently. Where in one spot there may be huge peaks, in other places there can be nulls, where bass at certain frequencies is very low in output. Some people use this to their advantage and place a sub in the corner ro take advantage of the bass peaks that are most pronounced there. You can get more output with less power in corner and then eq out the peaks thereby allowing your sub to be more efficent.Because of the way room modes behave, howeer, it may be best to have speakers and seating locations at odd number measurements. Bass tends to "pile up" at even number locations because of the way bass waves travel. This is an over-simplification but basically what happens. For example in my room, I place my speakers at locations that are 1/7 of the length and width of the room. For example my room is 24.5 feet long so my front speakers are 3.5 from the front wall and 2.4 feet from the side walls. My seating location is about 14 feet from the front wall which is about 4/7ths of the length of the room. This is not exact but it gives you a ball park to start as to where the best seating locations and speaker locations are in a room. You may have to move the locations slightly forward or back to get the flatest responses from you audio system. Of course you can just ignore most of this advice and just buy a Velodyne SMS-1 and use the mike to measure at your seating location which will correct most but not all of your room modes.
You'll get the best result if you are able to do multiple things like eq, seating position, and speaker placement.
