I have a Lenovo TAB4 8 Plus tablet (generally excellent) with Android 8.1.0 OS linked via wi-fi to a newly-purchased SkyEcho 2 tranceiver. As I have the older-version Bose A20 headphones, I have to use a 3.5mm audio jack to link headphones with tablet - Bluetooth only works with a phone. I've gone through all the various SD settings top to bottom (Navigation Settings > Produce Speech for Warnings [enabled] Produce Sounds for Warnings [disabled]). In SD simulator mode on the ground with the tablet connected to the office/home wi-fi, I can see traffic/hazard alerts on the tablet screen and hear the same through my headphones; in-flight, with the tablet connected to SkyEcho, I can see the alerts, but hear absolutely nothing. 

Anyone got any ideas or had a similar problem? If it makes a difference, I've disabled the 'Auto-off' function in the A20 Control Module which basically means the ANC doesn't now turn off during periods of inactivity. 

TIA.