If you view the contents of an audio CD from Windows, you'll see that it contains a number of .CDA files each corresponding to a song track. (CDA BTW, stands for Compact Disk Audio)
Why you can't copy these files to your PC rather than first having to rip them to .WAV files. There are no .CDA files on a CD. In fact, from a Windows perspective, there are no "files" at all.
An audio CD differs greatly from your hard drive or floppy disk drive in the way information is stored.
These devices store data in concentric rings called tracks. In contrast, audio CDs store data in a continuous spiral starting from the inside of the CD and ending at the outer edge of the CD. Kind of like a vinyl LP in reverse.
The format of the data stored on CDs is also quite different; it's a raw 16 bit digital PCM stream rather than a format that can be recognized by a Windows PC.
So what are .CDA files that you see on an audio CD?
These files are created by the Windows CD driver. They are simply representations of the CD audio tracks and are not actually on the CD.
Each .CDA file is a kind of a pointer to the location of a specific track on the CD and contains no musical information. They are all 44 bytes in length and each contain track times plus a special Windows shortcut that allows users to access the specific audio tracks.
So if .CDA files contain no musical information, what happens if you "copy" a .CDA from an audio CD to your hard drive and then double click it?
If the CD is still in the drive then the corresponding track will play from the CD. If you remove the CD you will get an error message. That's because the .CDA file contain no music, it only point to where the music is located on the CD.
To work with audio files on your CD you need first to convert them to .WAV, .MP3 or another file format that computers understand. That's what a CD ripper does and that's why you must use a ripper before you can work with your audio files. Simple as that.
Make a Image of your Audio + Data Disk.
Open the Image with an Iso Editor.
Edit the Image by adding your chosen music files in the appropriate form.
Save the Image
Load this Image with a Virtual drive. (Mounting) and copy protection emulation maybe needed and these programs provide that for you.
Mounting simple means that your are emulating as if your were putting a cd in the drive.
Play your game with you added tunes. When your are finished unmount the image. When you want to play again mount the image. No more playing around with your cd.
*** Note - Depending on the programming code contained you should be able to have your music at least play but the interaction within the game that you are playing may not necessarily work correctly without changing the programming code. ( IE: If your game displays what song is being played and by whom. )