I've done 5 formal demo's of the Tape Project tapes so far (3 of them 2 day affairs) with probably an average of 25 individual headphone listeners per day. The two tapes that easily get the most ooh's and ahh's is the A tape of both BlackJack David and the Arnold Overtures. BlackJack is the most asked for but the Arnold really has the ability to break barriers with folks that never listen to classical. Both are great demo tapes but for different reasons.
I think that the first two cuts of the Dave Alvin are particularly good at showing several of the great things that these tape can do. The way it begins so simple. I can't tell you how often listeners will say "Oh my god, that voice is just real!" And then it builds and at that point when the drums come forward if there isn't some nodding or toe tapping, there's something wrong with them or my rig.
With Abilene there's a more complex texture and the dynamic peaks really separate the men from the boys since you can hear all the instruments involved should sound clear and unforced in those peaks. If those peaks get hard or blurred, you have some refining of your playback system to do.
Like I said, the Arnold Overtures, particularly The Smoke, is a great "crossover" demo. I've never seen so many listeners who are totally unfamiliar to classical sit through the entire piece literally glued to the spot. This is obviously much more demanding of the system than the simple combo stuff and many go out and find a copy to use in their own for demos/tests of their own systems after hearing it. Great stuff.
Of course for jazz fans, just the mere mention that I have a tape of "Waltz for Debby" brings them running. At the last demo (CanJam 2009) I played it almost 5 hours straight.