Not my favorite genre, but I'd test out some classical piece that you're familiar with. Preferably with a wide dynamic range.
I'd probably play something off the Star Wars soundtrack
Convert the flac to a VBR mp3 on normal mode. This is what a lot of paid downloads would be at for quality.
To be fair, put both songs in playing now.
Turn on auto-repeat.
Minimize MC or turn the power to your monitor off.
Go eat dinner.
These two versions of the same song will have been repeated a for a while by the time you come back.
Idea being, you don't know which one is currently playing and start with a totally blind test.
Now, put in the earplugs.
Listen to both tracks in their entirety.
Which one did you like the best?
Could you tell any difference?