This Christmas I'd treated myself in buying the AKG 518 headphones as my local audio retailer (RicherSounds) were selling them at a 40% discount.
I have them hooked up to an IPOD classic 160GB with the FiiO E5 portable amplifier listening to R&B, Jazz, Rock with a dash of Hip-Hop and Classical depending on mood.
Firstly using the AKG 518 with the FiiO E5, my first observation is at that, the sometimes woolly bass is tighten-up whilst having the same kick.
That said the AKG 518 doesn't particularly scale well with the Fiio 5 portable amp i.e. other than the bass being a bit tighter, I can discern no other audible improvements unlike with my other-to-go headphones being the Philips Downtown over-ear, which when used with the E5 offer a big improvement in sound dynamics as well as volume.