I hve spent plenty of time experimenting with my Quad 33/ELS 63 setup with the sound sources of its generation - CD players - my Ipod and my tiny .mp3 player. I usually use the latter on their own with some humungously expensive headphones plugged in and get excellent results, but when comparing these devices with a computer playing back a .wav file or the CD player there is "something" different. If anybody played back two tracks to me and asked which was the .mp3 and which was the .wav I could not tell, except that they were slightly different, which suggests that probably the best original source these days for sound is an appropriately decoded .wav file. This again would suggest that sourcing in this instance should be some form of computer with a very large HDD to carry the .wav files. Of course if your ipod carrys tunes that you have downloaded, these will be in a compressed format anyway so I should disregard the above.
P.P.