I can't detect the noise and sound degradition in earbuds quite well, but i found that either the mp3(i use cbr 256) and WMA(160-192k) playing on a car stereo(using DAP headphone output to the stereo) give more distortion(i think is digital HF cutoff, CD plays well) than earbuds

While i'm not exactly sure what your setup is, there could be a quality degradation going from your DAP to the radio. You could try putting an original WAV file on your DAP, along with the MP3 and WMA copy of it, then listen for differences again. Testing MP3/WMA from DAP -> Line In on the radio against direct CD playback on your radio is not really cutting it.