both measurements if they are right, show great sound for portable(specially crosstalk is often really poor on portable devices), you mustn't put that against manufacturer's specs, all products pretend to do 110 or 120db SNR, that's a load of crap. they do that in the digital domains, or at the amp section output only with no load, or with the ideal load etc.
but I must disagree with your explanations.
SNR is measured on those test with a certain voltage, that forces you to push the DAP really loud and a LOT louder than what you would use on IEMs. so when you'll use your IEMs, having a SNR or -70db instead of -90db, will make the hiss 20db louder and more likely to be heard under some circumstances. simply because lowering the volume is not bringing all the noises down with it. so in effect you can very much end up hearing the noise clearly with very sensitive IEMs on calm passages while listening to average loudness. because say the measurement was done outputting what would be 90db for the IEM, when you're listening calmly at say 70db, that will mean some of the noise is now 20db loud on that particular IEM and you will hear it on silent passages.
but still usually when the SNR measures better than 75db on most RMAA, it means most people will never mind any noise. only the ones with really picky stuff(togo 334, se846...) should really look for better specs or simply get an amp that has better specs. and that's what lachlan is saying I think. he's bummed out because he expected the sound to go with the price, but it's the look that goes with the price the most.
I also disagree with the higher resolution being more accurate. while it's true in the end(at least for higher sample rate), it's usually not audible as what it's improving is usually some noise well below -80db. so from 0 to -80db from 20hz to at least 16 or 18khz(depending on the roll off filter) the sound is 100% the same in 16/44. that's why people fail blind tests. I won't start a pointless war and people who feel they can hear improvement over hires should just use hires. but the improvement will be way down below the music itself that is as you said often in the first 50 or 60db of dynamic.
now while I'm saying all this, those measurements seem to show stuff well below all this and well below audible range so to me they both should sound very transparent and the same indeed on most heasy to drive headphones at least. and it's not a bad thing, it only means that we have at last reached transparency in portable audio. now we just have to concentrate on driving power and getting the right amp when it's needed.
I sure would love my cheaper DAPs to have the noise and crosstalk values of the ZX1.
