Smile [Q] Music with Bluetooth hands-free kit with Sony Xperia Z2

Hi everyone,
Yesterday I purchased a white Z2 and I have a little problem: when I listen to music with my hands-free kit, the music is quite slow and is of poor quality. I connected my hands-free kit to iPhone and play will start perfectly. Then I started playing music from the Z2 and I listened for wired headphones, the music is perfect. Finally, I connected my Xperia to my bluetooth hands free kit with wired and sound is perfect so it affirm a bad parameter in sound in Bluetooth. Can anyone help me if there is a particular configuration for a bluetooth hands free kit? I'm sorry for my english not very good I'm French.

Thank you everybody.