Complex sentence: The Arcade Card Pro was specifically for pre-Duo systems although it was compatible with all PC-Engine systems (including the SuperGrafx), it included both the SuperCD operating system and the extra memory found in the Duo systems.
Split into simpler sentences: The Arcade Card Pro was specifically for pre-Duo systems although it was compatible with all PC Engine systems (including the SuperGrafx). It included both the Super CD operating system and the extra memory found in the Duo systems.