Dell unfortunately has many desktops to choose from making decisions like these more difficult.
The Inspiron desktops tend to be more low end, but are capable of streaming movies and music. Studio desktops are made for multimedia and the Studio XPS is a more high end multimedia system. Alienware desktops are more for losmovies (losmovies.stream) gaming and would be overkill for internet streaming.
The Studio XPS is a very good deal for a desktop and is very capable of streaming movies and music, but if you want to save money go with a studio desktop. I hope this helps guide you decision. Good luck.