I'm interested in knowing if many people use the site...JRiver.com...for music downloads, etc.  What are the pros and cons?

Which online sites provide music uploads of CD quality or better?

Curious as  to why at Amazon the Beyerdynamic DT-990-Pro 250 ohm model sells for $167. and yet the non "Pro" 250 ohm version sells for $302.  ?? 

I want to know if the high quality, not MP3, music I download to my laptop can be listened to with headphones, DAC and amp?  Or does the fact it is on my laptop degrade the quality of the music?

My first time on this site but the reason I'm here is to seek some help in obtaining a good but not esoteric, pair of headphones.  I've read several reviews but it seems to be subject to individual tastes.  I am also concerned about comfort, I've got a large head.  So if I can get some direction...