Clip+ Car Audio

My car stereo has an auxiliary input. I hooked up my Clip+ this morning, and was disappointed in the quality.  Not awful, but very inferior to what I’m used to from MP3 CDs played on the same stereo.  I tried it with volume at full and half.  Even at full volume, I had to turn up the volume on the stereo quite a bit beyond normal.  With the Clip+ at half volume, I had to turn the stereo almost to full volume.