BoneSnapDeez wrote:One thing that still confuses me...
I have a PC Engine Duo. Will I ever need any type of system card to play certain games? Or is the extra RAM "built in"?
You are set for regular CD and Super CD games. If you want to play Arcade Card games (Sapphire is probably the only real noteworthy exclusive, and it goes for a few hundred dollars), you'll need an Arcade Card. Don't worry, though, you are set for like 95% of CD games already. This was all explained in the first post, but I know that's a lot of info to digest.

I'd say it's not really worth it to get an Arcade Card unless you get very hardcore into PC Engine collecting.