My friend was telling me about his high-end Marantz cd to cd-r copying/player unit (CD Recorder DR 6050) and how it would only burn to certifited Audio cds. Never having heard of such a restriction, I tried copying a cd using a Ritek cd, and was rejected (the display said “USE AUDIO CD”).
Does anyone know if these “Audio” cds are really anything special/different, or is there just some header info on those cd-rs that locks consumer out of choosing cheaper media?
Yes, some header info, but maybe not to only make you buy the more expensive, but sometimes recorder might not let you copy “audio cd-r”, or there might be some royalty going to Recording Artists organizations when you buy audio cd-r.
Can you try in your friends machine if he can copy a audio cd-r copy?
EDIT:
I did some search, this is the full answer 
http://www.barrel-of-monkeys.com/graphics/prod/dvdplayers/scms.html
Whoa, nice job, detective. That is a good article.