You'd never know from how 'little' we harp on about it, but iPods aren't exactly the best sounding media players on the market. As a result, if you care about quality reproduction of your audio you'll probably be inclined to sacrifice their admittedly impeccable user interfaces in favour of a player better suited to do justice to your music collection.
While Apple might not make much effort to improve the iPod's audio processing itself, the company does seem happy for third parties to do something about it by way of the iPod dock connector.
For instance, the dock on the Onkyo ND-S1 Digital Media Transport can tap directly into the digital files stored on an iPod thereby bypassing the player's DAC and amplifier so they can be decoded elsewhere. As such you could plug in an iPod classic, fifth gen iPod, any gen of iPod nano, iPod touch or even an iPhone (in flight mode) into the ND-S1 and the quality of the audio available will be dictated not by the version of iPod you're using, but by the quality of the digital files stored therein, and the system to which you are sending them.
The ND-S1 isn't just a one trick pony, though. A quick peak at its rear shows not only a power input and both coaxial and optical digital outputs, but also a coaxial video-out and, more interestingly, a USB-B port. You might expect that this makes it possible to connect any docked iPod to a PC and sync with iTunes and indeed it does. There's even a button to toggle this mode on or off should you desire.