amarra or pure music..?

Bbopman - The only thing that can change sound, if digital file is the same, is jitter (it was verified by Stereophile that Airport Express transmission is bit-perfect).

Music stored on the hard drive has not timing. Music is transferred to AE compressed (ALAC) in packets and buffered (few seconds buffer). Timinig is created by AE. I cannot imagine how playback program could change sound with wireless AE unless CD was ripped differently (Itunes does not rip bit-perfect).

Audirvana Plus has, for example, the Izotope 64-bit resampler. Multiple dimensions of configuration which allow you to do things like apply a minimum apodizing filter. So aside from jitter, there are some things that may affect the sound.

Wilsynet - It is possible that processing of standard CD will change sound but Airport Express is limited to 16/44.1

I have purchased decibel, pure music and amarra over 1 year.
I was very skeptical about Amarra since it is expensive and I was not sure
It will make that much difference. A few days ago, since Amarra has special sale I downloaded and tried it. (mini version).
I have to say "Wow Wow". It gives a lot more deeper and wider soundstage and high is REALLY smooth and has more air. IMO pure music has slightly tighter base but has glare at high to compare with Amarra and decibel is as smooth as Amarra but it has less definitive image and sound stage shrink a little bit to compre with puremusic. Amarra make the music much more enjoyable for much longer time. I still do not like their license limitation and price but I purchased Amarra mini without hesitation at this time at $195.
The sonic difference is not subtle. It is big diffeence IMO!

For what it's worth, I think Audirvana Plus sounds every bit as good as Amarra and is only $49 and unlike Amarra, Audirvana is much more stable and reliable.