Coding audio streams to Airport Express?

Not even sure where to post this question, so my apologies if this is too far off topic.
I'm very curious about the audio coding that happens when streaming music from iTunes to an Airport Express, or, a 2nd gen AppleTV? Is there any additional code-decode going on when streaming? Playing a 44.1 kHz .wav file, uncompressed, and capture that waveform at the electrical out of Airport Express... will it be identical to the original .wav file (ignoring some minor D/A artifacts)??
Many thanks in advance.

Can you reference a link or 2 where I can read a bit further?
I'll see what I can find as Apple has provided very few details on this. The links I had to some material I had reviewed earlier, unfortunately, are no longer valid.
For example, what happens with an uncompressed .wav file that is an 11kHz sample rate? Does the AX have a D/A that supports all of the supported sample rates? Or, is that part of the compression "on the fly" into Apple Lossless that everything is coded / converted into a single sample rate (44.1 kHz??).
Great question!
The AX works only with iTunes v4.6+ and is limited to music files that iTunes can read; ie, 16-bit data only. (An exception is you can use a third-party product like Rogue Amoeba's AirFoil to stream other non-iTunes sources.) These data, though, can be in any file format that iTunes recognizes, from lossy MP3s at the low-quality end of the spectrum to Apple Lossless and lossless AIFF or WAV files at the high end. To more directly answer your questions, the AX functions only at a 44.1kHz sample rate. When you play, for example: 11kHz, 32kHz or 48kHz data, iTunes sample-rate-converts the data in real time before sending it to the AX. As you figured this is a limitation of the QuickTime Codec that is the heart of iTunes.
One operational glitch, that primarily affects the analog side, is the fact that the AX doesn't have a local clock circuit. When the incoming data is interrupted, as it is when you change songs in iTunes, there is no longer a digital output to feed the DAC, which loses lock as a result. Provided you can live with its limitations the combination of iTunes and an AX provides an easy way to pipe CD-quality music around your home.
FYI. For the 802.11b/g version of the AX, the analog audio is handled by a Texas Instruments PCM2705 digital-to-analog converter. I don't know if they used the same DAC for the newer 802.11n model. Some audiophiles use an external DAC in an attempt to overcome any of the AX's shortcomings.

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