Yeah, I changed mine out for the velours and find them much more comfortable. I sweat easily, so the pleather ones were always getting damp.
They are a bit of a stretch, but it looks just fine. You basically just peel the pleather pads out of the grooves around the edges of the cups. They should slip off with a bit of finagling. You install the new ones by reversing that process.
When I ordered them, it took about a week but there was no mention of delayed shipping.
I use mine out of an iPod Classic 160GB and it works just fine. When I hook it up to a full-amp, it sounds better and fuller, but you'll get about 80% of the performance out of the iPod Classic. When I hook it up to the iPod Nano (current generation), it sounds really thin and the volume needs to be turned all the way up.
I'd imagine the Cowon players will be better at driving the 580s un-amped. I don't have any experience with them other than the two that I listed though as I'm really not very knowledgable on the subject of DAPs other than the two that I own. Hopefully someone else can chime in with their experiences with other DAPs.