Since we don't have a CD player or an AUX jack, I have used .WAV files of pink noise for checking stuff with an RTA. I just looked at some of the files and they're 16-bit 2-channel 44100 Hz. As long as your files are that format (which anything ripped straight from CD will be, AFAIK), you should be ok.
Since they're such big files, though, I'm guessing you may have them on a large USB drive, and I've seen some threads here about slow reading of large USB drives. Though I'm not sure if that was due to the drive size or due to a huge number of files on it (I would think the latter).