I am getting a Duo-R shortly and I was wondering, does all Duo have internal 3.0 support and not need the card? I am going to replace my existing TurboGrafx 16 and TurboCD setup because it's older and because it's rare to have matching serial number on CD base and CD drive (they always matched from factory but gets mixed up over time when people buys replacement drive or base) and I wanted to put them back in the original CD system box I kept. Beside Turbo CD doesn't handle CD-R well anyway. Duo is a bit more friendly and I've always wanted to play Space Fantasy Zone game.
Yes, all Duo integrate a full Sys Card 3.0. The only card you would need (if you care that is) is the Arcade Card (Duo or Pro they both work, just get whatever you can find).
I think you actually need System Card 1.0 for the CD version of Altered Beast. But no one should ever play that version.
If the System Card 3.0 is the US version you should keep it with your TG16 CD since it too is valuable but even more so if together as a set. Atleast I would think so since the System Card 3.0 for the Turbo is not nearly as common as the Japanese version.
