Fernando,
Having the CS-506-1, I can tell you that it does not have a sub-platter. The platter is a one piece stamped metal unit that has an integrated rim for the belt underneath. You are right about the headshell however. I also have a CS-606-1 which uses the other style ULM headshell (the one with the metal piece on top). Each has a different 1/2" cartridge adapter. They also take different versions of the original, Ortofon made, ULM cartridge. I still have the ULM cartridge for the 606, but swapped the one on the 506 for an OM-10. As I mentioned earlier, it is a decent starter table, but there are certainly better options further up in the Dual line.
Steve