You will get sued to oblivion by the industry if you build this. There is a website that already did something sort of like this, TurnTable.FM, and they did a bunch of feature limiting stuff in order to play nice with the record industry but they were still running into issues IIRC.
I think you've missed my point, Darkmonk.

I'm certainly NOT talking about remixing published tracks without permission... And I wasn't primarily thinking of 'high profile' performers. Instead, you would find up-and-coming underground artists & producers who would use the site to promote themselves and their material.
Hence my use of the words
"tracks uploaded by Featured Artists". You would have an arrangement with the creators of the tracks. You would NOT simply rip a track off a Jay-Z album, (or whoever).
Every week (or month) you'd have a "Featured Artist of the week". Let's say you, Darkmonk, were an upcoming rapper. You would personally grant permission for the site to allow users to remix one of your songs. To that end you would supply the site with every individual track from your mix (Vocals, bassline, separate drum tracks, individual synth samples or guitar parts etc...)
Users would then take the individual elements and recombine them. YOU, the artist, would retain all rights.
Benefits:
(1) MC Darkmonk would benefit from increased exposure to the target market.
(2) HGear's site would benefit from immense credibility and increased traffic.
(3) The users would gain valuable experience and also get to demonstrate their own skills (possibly leading to the chance for further collaborations).
Furthermore, users could upload THEIR OWN home-produced recordings (of their OWN rap tracks), for other users to remix... thus stimulating ongoing creative interactions between what would rapidly become THE cutting edge underground rap site.
I repeat - at NO stage would copyright be infringed, because everything is done with the full co-operation of the artists themselves.
Hope that helps to clarify my suggestion.