Speaking from someone who has had a few ipods, u2 edition black and white display, ipod photo 20gb, 5.5 gen 30 gb video, ipod touch 1st gen, 2nd gen 32gb, ipod classic 160gb, and a 2nd gen 2 gb nano. I can safely say I the 5.5 is warmer than the newest ones, but i actually prefer the sound of the newest model even though it doesn't have the treasure wolfson dac chip. It has a flatter response IMO.
Which "newest one" are you referring to? The Classic 16gb? Or the nano?