The maps in nRoute are probably only unlocked to your Quest, so using any other Garmin USB receiver (GPS18,18x,20x) would cause nRoute to not display the maps.
Non-Garmin GPS receivers, whether USB or Bluetooth, do not output a data signal suitable for nRoute. It requires a Garmin specific data type.
However, either of these issues can be resolved with GPS Gate. It can take the signal of Garmin and non-Garmin GPS devices and provide a data signal compatible with nRoute's requirements. It also allows properly unlocked maps to work with other GPS devices than the original.
So, buy a GPS you like (e.g. USB Globalsat BU-353) and download GPS Gate.
Terry