Facing the low record volume with my SM-G900F, although I've noticed that it seems to be a problem with WhatsApp voice recording. The stock recorder of my LOS 16 (use it with GApps pico) seems to have a decent volume. As for a flashable zip, I think we have to wait for someone who is capable of changing the installation scripts by adjusting the paths which seem to have been changed in LOS 16. When that is done, there most probably will be a backup and a micgain zip which we could test.
If anyone reading this can help with it, we'd appreciate it.