In terms of frequency response accuracy, it's likely not an issue, in fact, I would safely assume it as flat. Even cheap china-made imitation mp3 players can achieve a flat freq response.

The real issue with portable players is the internal amp. Most mp3 player have an undersized amp, and hence is unable to produce a proper sine or square wave. Yes, even iPod is guilty of this. If you tried to square wave with an iPod, you'll get something which looks like a shark fin instead. So to TenSpeed, iPod is really far from audiophile-quality.

Anyway, you just need a square wave file, and your ears and you'll get a good idea how the N810's amp fare.

However, just from the hiss alone, I can pretty much guess that it's an undersized amp too.