Personally I like classic rock and listen to a lot of the secular kind.   I don't think you can tarnish the entire 'Rock' genre with thoughts of Satanic influence.  I've not listened to much Christian rock, my knowledge of music in general is limited, both secular and Christian.  However I do think it's all down to personal taste, if the lyrics are filled with apparent 'satanistic' and 'evil' verses, then I think it's pretty clear you should stay clear.  But there are many different forms of music and how it's created, what one person can listen to and enjoy, another person may dislike strongly and prefer a much more opposite form.  So I don't think you can say there is a right or wrong if we're talking 'Christian' music as hopefully, the artists in proclaiming themselves Christians are focusing their music on giving God the glory of it.  If a certain kind of music gets you focused on God, then I can't see how thats a bad thing.

As for MWS, I'm not sure which album your talking about, however I used to be a huge fan.  Haven't heard much of his more recent stuff, but as for his older albums, I've quite a selection of his stuff and really enjoy it.  I've never really 'fed' into the idea of 'hidden' messages put into songs or that playing music backwards would produce a much more sinister agenda.  I mean for one, who on earth plays their music backwards? And if it were true that messages could be syphoned into a track of music, I'm sure some of the larger powers running the countries would certainly used it to their advantage.  Sound a little over the top? Not anymore so than thinking hidden messages are laced into music tracks.