As long as the 533 can still tune the same content except on diff. ch. #s, you should be OK.
The Mags have a diff. kind of tuner than typical HDTVs. It's a "hybrid" (switched) analog/digital tuner compared to the HDTV's integrated tuner (all channels in numeric sequence with no switch between analog and digital).
Comcast apparently changed the channel data (PSIP) that tells HDTVs how to tune each channel, and the Mag is interpreting that differently. Many people on cable have the same question and apprehension.
Just be thankful that Comcast hasn't gone all-digital in your area and scrambled all your channels, or they did go all-digital and decided to leave certain channels "in-the-clear"?
Another major pain with this Magnavox's weird tuner is that when the cable company changes the raw am numbers you need to hunt through them all. My cable company shifts the subchannels all the time' at least 2x a year. I often find that my recordings have picked up the wrong channel or nothing because my channel is now on a different sub channel. My TV's seem to figure this out on their own, but on the Magnavox that burden falls on me. I update my list translation list of raw qam channels.
I was hoping that they would have updated this odd tuning so that it would use the numbers like my TVs do because if they did I'd buy a new one today. I'm the only one who will use this box because nobody else will bother translating the channels even though they have printed lists and a link on their cellphone.