There are two music sites offering a selection of music, recorded in different formats, with which to test your DAC. Both are free, but Sound Liason based in the Netherlands, requires you to register. The other is Blue Coast Music
One advantage of Blue Coast Music that a new track is offered each month
http://www.soundliaison.com/all-categories/6-compare-formats
https://bluecoastmusic.com/free-downloads
One advantage of Blue Coast Music that a new track is offered each month
http://www.soundliaison.com/all-categories/6-compare-formats
https://bluecoastmusic.com/free-downloads