I just rip it off the CD in a non-lossy format. If you have a 320kbps MP3, that is, IMO, probably good enough for most uses, though.
The thing to recognize is that the reference track's already at a mastered [loudness] level for CD, which should be considerably higher than your mix bus, so you should use clip gain, or a gain plugin, to equalize the loudness as much as possible (i.e., by lowering the reference). There are still going to be differences because of the compression and limiting that may have been applied in the reference's mastering, but with the volume/equalized "normalized" to the mix, getting a sense of whether you're in the ballpark for the style should be doable.