Audiosex. Purely on the grounds that your link doesn't work, and I can't get to the website via any search engine.
"Note that while you can edit, mix, add new tracks and record, Studio One will prevent you from exporting a mixdown." So what exactly is the point of this service? You pay them to purchase the multitracks, load them into Studio One and then what.....sit and stare at them and realise you have wasted $10?
That depends on whether you're looking just for some stems or stems from famous artists. In the first case, yes, in the second maybe not better but just different.
Additionally this seems to be for Studio One only: A My.PreSonus account is required in order to use Mix The Music Multitracks in Studio One ... Once your Mix The Music and My.PreSonus accounts are successfully linked, you will find download links and a license key for Studio One ... If you do not already have Studio One 4 installed and activated, download Studio One
Maybe http://pro.beatport.com/stems, http://www.junodownload.com/stems/, http://traxsource.com/genre/28/stems, https://www.whatpeopleplay.com/stems
