"Most audiologists say the only real way you can tell there's a difference between one format and another is by giving the listener a double-blind test, where neither the subject nor the administrator knows which is which."
Not quite - a double-blind test is the only way you can *prove* there's a (distinguishable) difference.
Assuming that you haven't been deafened by your ipod already, most can distinguish between 128kbps and lossless on any decent pair of headphones (ie. not supplied with your player). Of course, if you have tinnitus caused by tin-can speakers I can only feel sorry...