Fact is CDs do not have a mix of polarity, the vast majority are inverted. Lots of coverage of this online, the link below is to one of the most well known sites. Changing polarity on my Paganini is a pain so I set it inverted for the majority, I try not to use the polarity change switch on the amp if I can as as another commentor pointed out it does change the active circuit. Just occasionally I find an LP that benefits however, for example yesterday on the "Breaking Glass" S/T (no great recording but inverting really helped)
http://www.absolutepolarity.com/
http://www.absolutepolarity.com/