Reality is defined by system resolution.
05-27-08: Chadnliz
...in reality it is very subtle to not even detectable far too often.
The reality is that each listener will have a different idea of what is detectable since his/her system's resolution will differ from others.
Until system resolution is increased, differences in sources will be subtle, if undetectable.
Here's an example. Until yesterday, I was considering selling my MP-1 preamp. Not enough midrange and bass weight...yada, yada, yada. Then, I swapped in a new power cord on my digital source (APL Denon 3910). Whoa. The midrange and bass returned in spades. One power cord swap made all the difference, and it was not subtle. If my system was less resolving, I doubt I would have had any issue with the MP-1 to start...let alone heard a difference in a power cord swap on my digital source.
Please understand I am not criticizing anyone's system. I only know from my experience how perception changes as equipment changes. I completely understand why someone would say changing digital sources would not make much difference, and I suspect this is true for the OP, but this observation cannot be generalized to all systems or system elements.
(donning the Nomex now...)