The Shure has a more neutral sound signature. The Denon D600s mids and highs are recessed. It sounds like you would be paying way too much for the D600s. I think $200-250 is what you should aim for, for the D600. That is unless you are finding the 1540s for much less than $500?
Reasonable price here ATM;
http://www.dwidigitalcameras.com.au/astore/Denon-Music-Manic-AH-D600-Over-Ear-Headphones.aspx#
I paid $285.00 for them only a few weeks ago. I'm still happy with them and I don't think they deserve the bashing they receive as for specific genres they are very good. I find the bass to be deep and powerful with no distortion to my ears. I am however mindful of the quality of the material they are fed ie, material with great production attributes for example Steely Dan and Donald Fagan. Daft Punk's Giorgio by Moroder sounds sensational on the D600's.