.cda is just the file extension used for audio CDs. .wav is the same thing, but with a PC extension. Basically, when you burn .wav files to an audio CDR, it does whatever it does and burns the PC files as audio files (.cda).
If you were to burn a data CDR containing your .wav files, the extensions would show .wav, but you couldn't play this in a CD Player - its not an Audio CDR.
EAC will losslessly extract the audio data from an Audio CDR to your PC and save them as .wav. You can set up EAC to rename the files as they extract so you don't have to name them. Although EAC can produce lossless .wav file from CDRs, it is not 'perfect'. Extracting like this assumes the Audio CDR was burned without errors, etc. Audio CDRs don't have the same data verification that data CDRs have.
With that in mind, many folks convert to FLAC and then burn those FLAC files as data files onto data CDRs. Later, you can use WinAmp to listen from the FLAC files directly, or convert the FLAC files back to .wav for burning to Audio CDR. This way, every Audio CDR is a perfect copy of the original (assuming there are no burning errors).
ETREE has a crap ton of info about this...
Terry