Marc,
I'm not sure about the Rotel RCD-855, as that is what I have, and mine is not an S1 (it may be an R1, I'd need to look at it again). Some lists show this as a TDA1541, not TDA1541a. It most definitely is an "a".
Hence my request to spritzer that I'd take those lowly S1's off his hands for him
Your plan of listening to plain TDA1541as is probably about the best you can do now, particularly given the fact that any double crown on the market would be suspected fake. There was a guy on pinkfishmedia that was testing some S2s for a potential group buy and determined that the ones being tested were not any better than the known good plain ones he was testing against, so he advised to abort on the buy. You might be able to determine what he was using to test however.
http://www.pinkfishmedia.net/forum/showthread.php?t=40114&highlight=1541a&page=6
Oops, this was S1 vs. plain. Still some valid bits however.