Keep this in mind:
If I want to buy a book or movie I visit Amazon. If I want to buy music I use the iTunes Music Store, if I want to buy a game console, and I don't know where they sell them.. I use google and gaming sites.
If you say you want to develop one website with all those products. However, I don't think that's an added value itself. Try searching for the current problems potential buyers have and create solution for that.
MediaAlley sounds to me, more like a youtube.com style gallery of videos and sounds. That's quite a "hot" area at the moment, perhaps a little too saturated though but the name fits quite nicely.
I'm thinking along the lines of "Meta Search for Media" depending on the parameters that the user types in the search, your site look at all the sites out there delivering the content that the user is requesting and delivers the best results pertaining to audio/video. At the same time, give users to share their own content along the lines of youtube.
The problem you'll encounter is that reinventing the wheel is next to impossible, yet you can try push the wheel further.
While google is probably the most accepted search engine out there, i wonder if the key to success isn't in the positioning of your product/site rather than trying to create something "totally new". Is there a search engine that's positioned exclusively for "Media Content"?
I think i'm looking for the way of least resistance. Developing the site may prove to be challenging already, positioning is the even more challenging undertaking...