How good is the Airport Express inbuilt Digital to Analogue converter?

Question

How good is the Airport Express inbuilt Digital to Analogue converter?
I have just purchased a 2012 dual band Airport Express which has the combined optical/3.5mm analogue jack audio output.
This is to connect to my hifi seperate amplifier, which does not have an optical input.
This gives me a couple of options
a) just use a standard 3.5mm jack to phono cable (and use the built in DAC in the airpor express)
or
b) purchase a seperate DAC to convert the optical from the Express into phono and connect that to the amplifier
I will be sending 250-320kbps music to the airport express wirelessly.
Will I see much/any benefit in sound quality with option B vs option A?
I ask because option A is free (I already have the cable) and option B will be around £20-£30 depending on which DAC I were to buy (I would also need a new TOSlink optical cable).
These are the sort of DACs I was looking at.
Thanks, Chipstix

Answer 1

How good is the Airport Express inbuilt Digital to Analogue converter?
Please check out this stereophile article on the earlier AirPort Express. I understand that the newest version may use basically similar audio hardware.
I will be sending 250-320kbps music to the airport express wirelessly.
The AirPort Express Base Station (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 AIF or WAV files at the high end. It is also important to note that the AX functions only at a 44.1kHz sample rate. When you play 32kHz or 48kHz data, iTunes sample-rate-converts the data in real time before sending it to the AX.
iTunes uses a QuickTime CODEC to convert audio files to Apple Lossless, and then, uses AirPlay to send them to the AX. In turn, the AX uses built-in software that converts the Apple Lossless to an Encoded Digital Audio format. From there, digital audio is sent to a optical transceiver to convert the electrical signal to an optical one before sending it to the innermost part of the audio port. As you already know for analog, the AX has a built-in DAC to convert the Encoded Digital Audio to Analog which is sent to the same audio port.
One operational glitch is the fact that, as 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. Using an external DAC, which may offer better audio performance, may have issues with this glitch. Some DACs are more sensitive than others.