For those who were as confused by the above post as I was, the devices mentioned are as follows...
The
xav-701hd is a SONY car Head unit (Details on the US Sony website
here).
... and the
xa-nv200tl is an add-on "navigation module" for some Sony equipment, made by TomTom.
I cannot see it on either the UK TomTom website or on the US or UK Sony website, but there's a picture of it on Amazon
here
However, I did find
this discussion on Sony's own forum, which seems to say they are NOT compatible with each other.
XAV-701BT is not equipped with integrated TomTom navigation and is not compatible to use with XA-NV200TL (navigation module). Using this Navigation module will display no navigation in the menu.