I do not own a DUO, but I know 1 type of CD-R most old readers love.
Diamond Silver (ink) CD-Rs. They are expensive, nearly 1 dollar each in 25's, but they will burn at 8X (no higher or lower) perfect burns which can be read by old game systems better than using an old drive, old media and 1X. I backup all my scratched discs this way and I can tell you they work in the: Sega CD, 3DO and the CDI (as well as the PSX and Saturn). I can't see why they wouldn't work in the DUO since the reason they work is they are over 80% more reflective than common CD-Rs. They even will supposedly replace the disc (a lot of good it would do you) if they loose data on a 8X burn in less than 100 years. Althought I have never tried to push them for a replacment. Oh yeah, they also work perfectly in the oldest car CD players out there. Perfectly, no skipping!