I too have the same problem on i9505. Been running CM for over a year and regularly upgrade but the recent move to CM11 0715 Nightly corrupted my EFS folder and I lost my modem, IMEI, APN's etc. Of course, no EFS backup (know better now!) blah blah. The only way I could restore the modem was to install I9505XXUGNE5_I9505VNZGNF2_I9505XXUGNE5_HOME.tar which is 4.4.2. Modem back but could not turn on WiFi and no sound. Flashed CM11 M7 and modem and WiFi working but still no sound.
Dialling *#1234# produces and error saying "Connection problem or invalid MMI code".
Baseband version I9505XXUGNE5
Any assistance would be greatly appreciated before I end up with a divorce!