Well the music samples are very good taken at face value but as content on the “Epic’s” marketplace the only way to do it, to find out, is to do it as art content that serves a purpose is highly subjective as to be included as part of a much larger project.
Lets take the Mixamo character package for example. At face value they are very good and some even fall into the category of AAA level design but as a usable asset is not very attractive as to a game based on unique requirements as they are easily recognized as an off the shelf product.
So it’s a catch 22 situation where the popularity as a product is rather limited up to the point that it starts to get over used. “Oh Yah” by Yello worked great in “Ferris Bueller’s Day Off” but kind of got over saturated in other films using the same sound track at the time.
Star Wars on the other hand benefited from the works of John Williams and from his ability to produce a result unique to the movie that made Star Wars Star Wars.
The long way of saying that perhaps you samples are to good but with in a narrow scope of usability but is not reason alone as to not doing it as to the unpredictability of the fair market system 
As an artist you have to get your stuff out there to just see what happens and build from there.