It's true - I can't help myself. Once I noticed that the headphone-out on my 900HA was much cleaner than I had expected, I decided I needed to do some testing. Nothing too serious, as I have no plans to actually use an eeepc as a music source, but enough to satisfy my curiosity.
The setup was as usual: both sources connected to my DIY switch box, then into the PA2V2 amp and the MS Pros. I level matched the sources by ear using a sine wave, ending up with the ipod on full volume and the 900HA 4 steps below full volume (jack set to line out mode). The 900HA was booted into Windows, as the audio seems to be better quality. Both sources were playing WAV files.
The A/B testing was done fairly subjectively, without the usual rigour. Rather than having a certain number of guesses and recording the results, I just listened to a dozen tracks or so, switching back and forth, checking my guess, then re-randomising the input selection.
Suprisingly both were quite similar in sound, and it wasn't until near the end of the listening session that I identified the different sound signatures. The ipod was noticably smoother, especially in the mids, whereas the 900HA had a more live/harsh sound. By the end of the session I could pick the source around 8/10 times.
Despite being still very impressed with 900HA, the ipod subjectively has a much nicer sound. But it's impressive that a netbook that cost only slightly more than the ipod is so close sonically. Especially when every full-size laptop I've heard has utterly terrible audio.
As an aside, synching the tracks between sources was a bit of a challenge, as both had a slightly different delay from button-press to track start. I eventually got the swing of it, although never got it perfect. It's much easier to test amps than sources.