Ummm, if you don't mind me suggesting. Have you checked both repeater and main unit are both reading the same as in Nm, Knts or Kms. Km's, is darn near exactly half knts. So if the main unit is saying 10 knts, the repeater will only be displaying a figure of 5 km/hr.
Their Navbuss is a great communication tool. I can't see it being the problem. It works better than NMEA
and is simple. All data is shared on the Buss. Each instrument takes what Data it requires from the Buss. NMEA
is much more complex and less reliable. But it is an industry standard that allows differing makes of electronics
be able to communicate with one another.
I will see if I can do some home work for you and come up with suggestions. I do believe in this product. I am sorry you have had issues right out of the box. I just hope that the new owners are easy to deal with. Newbrunswick is the new owner and they are rather big. Which means it is not so easy to talk to the "techy out back" anymore.