An imaginary sound quality difference between identical binary data is indeed low down on my list of priorities. There might be a sound quality difference if the playback is not bit perfect, or because of buggy software and/or broken hardware, but once you have non-buggy bit perfect playback (something that can easily be achieved even with free players like foobar2000 on Windows), further "improvement" - particularly one related to sound stage, bass extension, or other non-sense, rather than something obvious like skipping, which, on the other hand, would fail to meet the requirement of non-buggy bit perfect playback - is almost always placebo, and in the rare cases when it is not, it is some kind of hardware or driver problem. I have yet to see evidence that audible "software induced jitter" is not a myth on anything other than pathetically poor hardware. It is the kind of stuff for the same people that believe in "huge improvements" from $10000 power cords, cable elevators, and all sorts of esoteric tweaks.
If you believe "bitperfect" = all players sound the same, that is absolutely your prerogative. Most people in this particular thread will not agree with you, as they have listened, and can hear, a difference. This is why I thought you might be trolling - come to the place where an intractably objectivist viewpoint would make the biggest "splash". However, you have every right to do so, as this is a forum, and disparate views should be expressed - though it might sound less like trolling if you actually directly answered the question being asked, and expressed less ridicule in doing so ... for instance, if you said "I have listened to one/several of these players and, in my opinion, the sound quality is exactly the same as iTunes".
Suggesting it SHOULDN'T make sense, and that it therefore doesn't, is quite an unscientific approach (not to mention a logical fallacy) and I'll note that you make no mention of being unable to HEAR differences. Or any mention of you having listened for yourself at all. Your point is that, given your current level of understanding, and what is currently measurable, there SHOULDN'T be a difference (kind of like how bumblebees can't fly, or how 16 bit CD's promised "perfect sound forever" - heck even "jitter" was an unknown phenomenon, and unmeasured, in CD playback less than 20 years ago ... it's just that some people could hear it even though it didn't exist).
Certainly, even within different builds of one particular player I can hear significant sound quality differences through the inbuilt DAC/headphone socket on a 2011 iMac using Apple's crappy iBuds (Try Audirvana 1.5.10 verses 1.5.9 - they are hugely different in sound quality - though the base code is exceedingly similar). I would welcome your opinion that there is no difference in sound quality, for you, far more if you mentioned some form of listening tests (I know - an actual TEST), rather than saying that you don't understand the mechanics of WHY it would make a difference and inferring from this that there is therefore, objectively and incontrovertibly, no difference.
Let's face it - you are not probably going to actually listen with an open mind, and you will argue that I am listening with TOO open a mind (leading to psycho-acoustic effects such as "confirmation bias" etc.). Though in this case, I hated the sound of the latest revision of Audirvana Plus and rolled back to 1.5.9 - even though I expected the new version to have better sound quality as it was promoted as having "sound quality optimisations".
It's easy enough to try for yourself ... it sounds as though you aren't using a Mac, so you can't try the two builds of Audirvana Plus I suggested, but how about comparing "iTunes" on your PC with something like a demo of JRiver or Foobar 2000 - no financial expenditure required on your part, and all can play bitperfect. If you can't hear the difference, then you'll be able to state objectively that it SHOULDN'T make a difference (which is still a bit of a modification from you stating categorically that it DOESN'T make a difference) AND will also be able to state that you tested it and that you couldn't HEAR a difference. This will make a far stronger, defensible and compelling position than arguing that we/you know all that there is to be known, all that can be known, about digital transmission.
However, just to take it back to the poster whose question I was originally answering, they COULD hear a big difference in sound quality between iTunes and Audirvana ("it worked wonders to improve the sound from the MBP hardware") - using only the built-in DAC and headphone amplifier of their computer !! Their question is whether such a sonic improvement (viv-avis iTunes) will disappear when using an external DAC. I guess your position is that they didn't really hear an improvement in sound quality in the first place on their MBP, and if they are delusional enough to think the sound quality improved on an internal DAC, they might be delusional enough to believe the sound quality will be improved on an external DAC - would this be a fair statement ? Or is it your contention that they DID hear a sonic improvement on the internal DAC, but this would not carry through to an external DAC as the bitperfect stream to an external DAC is somehow less "bitperfect" than the stream to the internal DAC ? I am trying to help that person who posted, and your alternate viewpoint would also help them by providing some balance. So if you could clarify how your statements might relate to their question, that would be helpful (ie. Is it that they didn't hear a difference in sound, or that they won't hear a difference in sound, or that they could with an internal DAC, but won't with an external ?).
