Nando -
I think the key words here are "up to spec". If the data stream is fine (as it should be) and it's strobed ok to the DAC then there will be no differences detectable except by expectation bias/placebo/sighted test problems and so on. If the transport is not up to spec then yes there will be a difference - I've no idea if the "sh**te" players you mention are up to spec or not - if so then they will be, in performance terms, equal to the best of the rest! Tests of files produced as in the above "bake off" would be most interesting.
I'm pretty much in favour of ABX blind tests to check these things out. This reminds me of an interesting AES paper (which passed peer review if I recall correctly, unlike a lot of the so called tests we hear about) containing fairly contentious results with reference to "hi resolution vs CD standard files".
Here's a link to the paper and a bit of background:
www.aes.org/e-lib/browse.cfm?elib=14195
www.bostonaudiosociety.org/explanation.htm
Quite amusing.