Those aren't schematics, they're block diagrams, neither one of which make sense. SD cards can generally use an SPI bus, which may or may not be I²C compatible and I don't know of any SD cards that use the I²S interface. So you would use the PIC to read from the SD card via the generic SPI interface (or implement a proper SD card interface if it's possible) and then use the PIC to communicate with the codec via I²C which you feed into your amplifier. You might use SPI to the SD card and I²S to the codec chip but it depends on your needs and the full capabilities of the codec.
Keep in mind there is very little reason to do such a project, consumer devices are so sophisticated plentiful and cheap, there's no need. If this is for a school project I'm not sure any teacher would do much more than give you a passing grade for doing it, it's the modern version of the old fashioned solar system model using foam balls. There is so much information available via Google for projects such as this that it's hardly worth the effort to post it in a forum.