No I haven't. Don't know if I've even got duplicates of any of my disks but I will check. My recollection from the various reviews I have seen is that some have done this.
I agree it would be an interesting experiment. If I can locate any dup. CD's I'll give it a go and report back.

I agree that there is certainly a "placebo" effect that can happen. I do however think it can have a real direct correlation to how much is spent. Those expensive battery-aided speaker cables for example; if I had laid out a fortune on this product I would sure want to "believe" it sounded better.

My ears are pretty certain I got at least my $40 worth in this case. And I have listened to music that I was most familiar with to start.

As I said we all hear what we will. It's a subjective audio world. Even if all the tests "prove" something is better, it still comes down to how it sounds to me, on my system, in my room.