It doesn't come with a 6 CD changer, but with the HDD built in, you can load around 25GB of music, so you don't ever need to use CD's again.
From my understanding, the H has a larger HDD, quicker processor and then the obvious benefits of more up to date firmware and probably maps too. And there is quite a difference in speed between the C & H thanks to the faster processor. It also seems that you can only go up to a certain firmware update on the older units due to the processor, whereas the newer firmware will work on the H.