Vigor 2600V poor speech quality

I have just taken delivery of a Vigor 2600 adsl / VoIP router. My first
testing showed it to perform very badly on outgoing speech, incomming was
fine.
I tried G729 and G711Alaw but there was little difference.
I was connecting to a Cisco AS5300 over a fast link so i don't think the
problem is on the network, also there was very little other traffic going
through the vigor from the LAN.
Has anyone else had good results from this model I wonder?

Regards
PaulC