@UXSam: It appears that you're using neither the software nor the DSP sbc encoder for whatever you're playing with mplayer. See Christoph's post above for what you should see in the output of "dmesg" if the DSP is being used (this is also repeated in the output of mplayer on the command line).

Because you've enabled a2dp? Try disablling it and the output should then be directed through the speakers (assuming you turn the headset off, as otherwise you'll probably get the audio output as HSP audio through them (in mono through both ears)).

If you are getting any working a2dp output, I'd guess you've not managed to install the bluez-utils package. I'll have a look at the file modification date for that and let you know what it should be.

Do you have a file named sbcenc.o and sbcenc.cmd in /lib/dsp/modules?

What is in your /lib/dsp/dsp_dld_avs.conf? (I think that's the right name, not gone the device in front of me atm)