I've actually put serious consideration into this idea before (also in Houston, weird), but I'm just not in a position financially to take the leap right now. My thought was that it could be a viable idea, but it would live or die on adding some value to the headphone experience above and beyond simply being a place in which headphones could be purchased. If you run it as just a shop with headphones in it, you're competing head on with the internet on price and that's suicide.
You would need several things to draw people in and keep them engaged with your store as an extension of their interest in audio. A good website with some forums that you could try to develop into an active community would be good. In store events like little classes/seminars on various aspects of audio or the advantages of headphones over speakers would be a good way to draw attention (a store in which something is obviously going on is more likely to draw curious passers by than one in which nothing is happening), convince people of the need for your product, and earn a little good will if you can really make it seem genuine as opposed to yet another bit of marketing.
The big uphill battle will be convincing the larger public to think of headphones as a lifestyle purchase, rather than as a appliance where you buy one and use it until it breaks. Fortunately celebrity endorsed headphones have already started doing this for you. Something like the Apple or Sony Style stores are likely to work best. The average person is likely to just walk right by what looks like another store for tech geeks.
Out of curiosity, which mall were you thinking about? The Galleria? River Oaks? Maybe Baybrook?
Anyway, those were just the thoughts I had when trying to put an idea together. Best of luck to you if you actually decide to move forward with this.