My interest is in optimizing a wireless link from multiple Apple devices to my main audio set. For that purpose I'm currently using an Airport Express directly connected to a pre-amp to unexpectedly good effect. How does the standard DAC in Apple's Airport Express (using Airplay) stack up to the best of the bespoke DACs? To phrase the question differently: how much quality gain could be expected from running the Airport Express' digital/optical out through for instance the Arcam rDAC 300 in stead of directly plugging into the pre-amp?
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I briefly ran a 2nd system with the DAC from an AE and felt I wasn't getting the most from it (audiolab 8000, B&W 685s). I 'borrowed' the Dacmagic from my other system and was much impressed by the result such tthat I could no longer listen to the AE DAC (once aware what I was missing), I tried a Squeezebox Touch as a replacement for the AE DAC and am very happy with the result sonically. Different to the DM but I wouldn't say either was better.
So, all subjective but I'd say the AE DAC can be substatially improved upon, detail was the main area of improvement for me, closely followed by soundstage.