I think the general problem is mid-range speakers and reasonable settings is all it really takes to have quality sound, but people want to be above average and therefore look for ways to discriminate between better sound and worse sound differences they can't "yet" hear. From there you get into placebo and random correlations.
It can also be your room. If you're not exactly located in the same listening position the listening experience can change a lot, even with the same setup.
Your room is basically an equalizer and should be regarded as a part of your audio system. That's how some Hifi sellers can trick you into more expensive setups, they just change the speaker positions or your location to optimized defaults. It's crazy how they can trick people.
A harder hitting snare can be caused by changes to the upper mids and lower highs, by anything that is located between you and the speakers, and then the later reflections of the room which also add up.
Aren't those the same? Put more joules into the speaker wire and more joules of sound pressure waves will come out of the speaker cone, which just means the sound will be louder (until you reach the mechanical limits of the speaker, of course, but no DAC in the world could possibly change those).
Not really. If you take some of the transients out of recorded drums they will sound lifeless, without "energy", but not necessarily quieter.
I never benchmarked my Yamaha CD-S300 to other devices, but its flyers and web site never says it's completely flat on the analog outputs. The reviews of the player notes that it has the distinct Yamaha signature too.
Also "Monitor" and "Flat" devices as their name implies sounds pretty flat and dull.
All-in-all you should consider taking response graphs of your devices rightmark.
For Widows there is Rightmark, maybe you could run the Macbook's output against a decent Windows DAW.
audio.rightmark.org
The difference is not one of loudness but of 'energy'. A snare hit played from the high-end cd player sounds like someone actually hitting a snare; you can feel there's actual energy in the hit, while the macbook out sounds flat, even at higher loudness.
I'm not sure what is the exact cause but I've always guessed that it comes from the qualities of the built-in amps in the DACs.