I have found that a subwoofer system can greatly enhance 2-channel stereo listening. I have a REL that I love. I bought my ex-wife a Velodyne sub for her system that seems to work well at her house.

Did you have any problems integrating a sub seamlessly within your system? I've yet to hear a setup in which a sub is well integrated.

A sub can be well integrated. It just takes effort and knowledge.

You have to start with a properly treated room. Wihtout this beginning you will never get good sound out of your main speakers, much less out of any speaker that produces from 100Hz and below.

Then learn how to set up a sub properly. There are many good soureces, such as Bob Katz's book: Mastering Audio detailing how to set up a system for audio mastering. Following these guidelines will result in spectacular sounding system.