The very best CD-Rs to use for CD32s are the ones with very reflective surfaces. I've found "printable" CD-Rs with the white top and a SILVER bottom (don't get CD-Rs with a blue shiny side) work the best. Fortunately for me these are very cheap, around $10 for a spindle of 50. Burn at as low a speed as your CD burner will go, just to be extra thorough