So the RP-21 deal fell through . What do you think of the 501's? I suppose they'd need an amp, but with an amp how do they compare to other 200-300 headphones? And what do you think of the K81DJ's...the ones I'm looking at are recabled. Well right now the A900's are still an option, as well as the AKG's potentially, and I can always wait for some cheap RP-21's to go on sale...what are your thoughts?