This seems to be a problem with Asterisk 1.6.1 not being able to define which codecs should be used for direct URI dialing. If someone knows how to configure that, please post it here so I can add those codec options to the outward dial settings.
I think that Asterisk use the general SIP config when URI dialing. Or, you can do some hacking to set the codec in dialplan. I put an Asterisk dialplan example below. This should do the trick but I canoot figure out where should it be in the Askozia webGUI.
exten => _9X.,1,Set(__SIP_CODEC=g722)
exten => _9X.,2,Dial(SIP/${EXTEN:1}@sip.myprovider.com,300)
Hope it helps you make the improvement.
Cheers.