Should the sound quality be the same whether the source is an iPod or a computer and would all iPods provide the same sound quality irrespective of the memory capacity? I realise that the speaker or headphone quality has a major bearing.
I think the quality from a computer would depend on the quality of the sound card and i would expect most computers would produce a lower quality sound than an iPod but as you say, the speaker / headphone quality would make a BIG difference.
Memory size is irrelevant. The type of file that is being played (mp3,acc,mp4) will determine the quality of sound. And if you listen to crap music... well, the best headphones will only make it sound ...more crap!