A simple solution is a smartphone support.  I use my iPhone with Waze or Scenic app (to follow a trace GPX).

Just joined the Club and saw this query posted.

I recently purchased a GARMIN ZUMO 396 LMT-S sat nav (the day after their birthday half-price offer ended !) It is designed for bikers and connects via bluetooth to a helmet-mounted headset. However, I have found it works well with a pair (or one - you can still have a conversation with the passenger) of A8 wireless earbuds (Amazon c.£20), although the Garrmin voice develops a slight lisp.A nice Chinese lady tells you if you are connected/disconnected (presumably - my Mandarin is not too hot). Boxed earbud instructions were in German, but are available in English on the internet.

Not tried them on the A8, but they appear to work well on the roads around Norfolk.