Fancy title for a simple concept. So, I am using Logitech Z506 5.1 system, http://www.logitech.com/en-us/product/surround-sound-speaker-z506
with my ASUS P8Z68 Motherboard which features Realtek ALC 889 7.1 + 2 audio controller. The problem is my down ported sub-woofer seems a bit too small for my tastes, it's only 27 watts RMS but it does have the potential and the power to fill up the room. I was quite content with it until I started messing with my Dad 2.1 Audionic system which features a decent sub-woofer that can really rattle some windows. But it's not that clean in terms of bass but it does give you that Cinema type feel.
Realtek chips have a very good feature called Jack re-tasking, in Windows Xp you could switch outputs in the back panel, in Windows 7 that is locked down but you can play with the front output (used for headphones mostly). I just took the woofer which does have it's own power and FM, USB etc input options as well and I simply plugged it in my front out and told my Audio controller to treat that port as a sub woofer out. Now, the beauty is that it will not mess up my other settings, it will just clone the sub woofer output and send it to the front output as stereo. Since the Sub assembly responds to LFE I don't have to worry about a thing, keep in mind the front out with the re-tasking is indeed sending sub woofer and center channel signals. The woofer ignores the center and just reproduces the bass.
The result is a complete cinema experience. My sound system now adds a powerful punch. I can listen to dubstep and literally feel my room shaking, I am not kidding the bass literally fills the whole room and it sounds amazing. It doesn't saturate the other channels since it's a isolated in some ways. But you do need to tweak it a bit, the volume has to be control otherwise you will have some unwanted feedback from the sub-woofers. And they both have to be normalized this can be done by focusing on the music reproduction and checking if it feels different. Since it's bass, you most likely will feel it.
Then it has to be consistent and the sounds MUST not be be booming in any way. I had this issue and I resolved it by lowering my volume and putting both the subs on carpet and moving them away from the wall as much as possible. Next power was adjusted, I was surprised to find that my little woofer which I accidentally set to 75 percentage BASS was taking the lead. The room was shaking (booming) but I felt something was wrong and I sorted that out. Now, it's a nice clean bass that fills the room, gives you the feeling of vibration, doesn't give you headaches and is ideal for watching movies or fucking with others.
UKF Dubstep works great, the kicks are intense.
In short, if you have a 2.1 system handy and it's not in use, you can use it's sub and combine it with your current system to add a powerful fucking punch. It's worth it plus it saves you money in buying a new system. My 75 watt Z506 is more than enough to fill up my room even the woofer on it's own is quite powerful, the new sub is only 30 watts and the difference is just 3 WATTS! One is down porting and the other is just the regular type. I am loving it
EDIT: it should be noted that this is ideal for people that wanted that extra punch, a normal tuned sub-woofer is more than enough for your needs but if you want to enjoy the action and your woofer tends to boom a lot or just doesn't give a clean bass on a high volume using this option makes sense.