i use the 2400, but i can start answering some of your questions...
first MK+PK stand for matte black ink and photo black ink so you need to use the profile which matches the black ink type you currently have installed, which should in turn be the correct choice for you paper, ie MK for matte papers and PK for glossy photo papers. check the manual for how to tell the printer whick black you have installed, usually in the printer setup software. and media type choices are greyed out when the printer isn't set up correctly for them (manual feed, sheet feed, front load, rear load, etc.). at least this is how the 2400 works and i believe the 4800 is similar in this respect. check the manual on "matching black ink to paper type", "customizing your print settings", and "selecting the correct paper type". and check your settings in "page setup" in your printing software, as well as print settings in your print software itself.
the printer setup will determine which papers are available and which are not (ie, greyed out).