First, there's no basis at all to the statement regarding HT subwoofers (what is an HT subwoofer?) and music systems. A well designed and implemented sub will work equally well in both and Hsu makes good subs. It can be argued that a sealed versus ported cabinet has better application in one or the other.
You can not go by what the manufacturer states is the bass response of your speaker. You need to actually measure your speaker's bass response in your room.
There are two basic approaches to integrating a sub: 1) bass augumentation and 2) bass replacement. In bass augumentation you attempt to augument the bass response of the main speakers. Obviously, this works better with full range speakers that are capable of producing clean bass. In bass replacement you use a crossover to high pass the main speakers and low pass the sub thereby moving the bass chores from the main speakers to the sub.
Either approach can work. I'm a fan of bass replacement because the majority of speakers are not capable of producing clean bass and perform better when they don't have to handle bass.
The THX crossover point for subs is 80Hz. As the crossover point is raised above this, the sound becomes more and more easily to localize. A sub can be localized, regardless of the crossover point, if it causes nearby objects in the room to resonate or if the volume is not matched to that of the main speakers. The key to integration is setting phase and matching volume.
Almost every system can make good use of a sub. There are very few speakers on the market today that have bass drivers large enough to produce clean bass. Also, being able to place a subwoofer independently of the main speakers gives it a huge advantage in obtaining smooth in room bass response.
Optimally, you should not know a sub is in the system until you turn it off and realize what's missing. If you know the sub is there, then the setup still needs work. It's doubtful that you can setup a sub properly without an SPL meter and test tones.
You might want to look at the Harman papers: http://www.harman.com/about_harman/technology_leadership.aspx
Click on White Papers and then these two papers: "Subwoofers: Optimum Number and Locations" and "Part Three: Getting the Bass Right".
As pointed out by Nick778, the Velodyne software is very useful. You might consider their SMS-1.
Best of luck.