I've a card reader for the ipad but it's just that, a reader - will not send files from ipad to card as far as I see. Don't think my Zumo will accept anything wirelessly but bluetooth clearly has potential (with a bit of firmware buggaration - waay beyond my ability tho'
A neat solution to that problem, is to use a RavPower FileHub Plus, Wireless Travel Router
https://www.amazon.co.uk/dp/B00TI3WQJS/ref=cm_sw_r_cp_tai_6gaGCbSTA8MZ8
Here’s how:
The travel router connects wirelessly (via its built in WiFi) to your iPad
You connect your Garmin Nav 6 (or Zumo, I assume it works as well) to the FileHub via the USB cable
The Garmin SD card mounts in the FileHub
You can transfer files from Scenic (Great app, that’s what I use) through the FileHub app onto your Garmin card, ready for import.
Very portable, great when touring and you only want to carry an iPad (or similar tablet) or even a phone.