I used JustDecompile to decompile and see how this thing was working. The problem is I needed fine control over when my stylesheets loaded and in which order. Since the Responsive Design has a bug where stylesheet files are applied across everything ruleset (this is a noted bug), I had to resort to my own code. Basically, I needed my desktop and mobile stylesheets to load in this particular order and the default CSS control widget (which used SitefinityStyleSheetManager) was forcing stylesheets I defined in it right inside the end of the <head /> tag, disallowing me to add my mobile stylesheet after the one from this control was loaded.
The order I needed was:
1. Base.css (in master page)
2. Interior.css (loaded in the CSS widget on my Interior template in SF, used by sub-pages)
3. Mobile.css, which needed to be loaded at the very end so that transformations could occur.
I ended up writing my own to bypass the built-in SitefinityStyleSheetManager, as well as load the stylesheets on Page_Load instead of Page_PreRender, thus allowing my master pages to give more control over when certain stylesheets loaded.
Sorry if this sounds vague. No need for a solution at this point as custom code (as always...) solved my problems. Thanks.