I think people make too big a deal out of the iPod's headphone-out quality. It's really not that bad, especially the most recent 5.5G revision. I've used the HD650, HD600, HD580 as well as the HD555 out of iPod headphone-out and it sounds good. OK, it may not be as good as amping the line-out, but it is still an acceptable and you will enjoy your music. The only danger is if your source file is not at a high enough volume, the iPod may not have enough juice to drive them to satisfyingly loud levels. I have never heard the iPod amp clip or make odd noises when driving tough loads (not even during the latter cannon passages of the famous Telarc 1812 Overture SACD recording).
Regarding aftermarket cables, I have only used one, the Zu Mobius on the HD650. First of all, it does not make the iPod sound more horrible. Maybe your Silver Dragon does, Ahobaka, but certainly not the Zu. Second of all, it is simply not worth the money if you're only going to be using an iPod as source. Better off using the same money towards an amp and line-out-dock of some sort.
I'm not exactly sure why you don't want to buy used. Almost every used piece of equipment I've purchased had been kept in near-pristine condition. They even smell new. Is that not good enough for you?