SRS Labs makes a variety of hardware and software products designed to improve digital audio. Their technology is built-in to a number of PC's and can be added to enhance the sound of headphones, speakers, etc. The result is greater volume, enhanced bass and treble, better separation, and an overall improvement in the clarity of less than perfect audio.
I purchased their hardware "adaptor" that works with the iPhone, various iPod models, and the iPad. Runs about $40 (with tax) from Amazon.
() The overall result is quite striking for streamed and stored music played over inexpensive portable speakers (iHome portable speakers, about $40) Increases volume significantly. So much, in fact, that I have to lower the volume on the iPad. Doesn't turn a $40 pair of speakers into $200 speakers but the quality improvement is substantial. Treble, bass, and separation can be adjusted independently via a free app from the iTunes store.
() The adaptor attaches to the iPad (and other Apple devices) through the 30 pin connector. Speakers or headphones then connect to the adaptor via a standard 3.5 mm headphone plug. This means the iPad cannot be charged simultaneously. That would not be a problem except for the fact that the adaptor increases the battery draw significantly. I'd estimate about 25% greater draw with the adaptor.
Products such as this, like speakers, are subject to individual preferences. Everyone hears music differently. To my ear, and with low end portable speakers, the improvement is substantial. Most, but not all, reviewers on Amazon agree. (Some find the "improvement" to be rather artificial much as some people prefer vinyl to digital music.) I haven't tried using the iWow-3D with my much better pair of speakers connected to my desktop system but I do have the SRS software on that system and the improvement with good speakers is similarly enhanced. So if you use your iPad with good speakers you may find a similar result.
Worth $40? I listen to music a lot on my iPad when I'm out and about. This little adaptor improves that experience but at the cost of substantial battery draw. That's the trade-off.