This is 100% an issue with the headphones. DAC stands for digital to analog converter. Because the Bluetooth connection is digital, it's the DAC on the headphones that handle they part of the equation. The same goes for the amp.
You could maybe find a music player that has a volume boost that modifies the digital output, but then you risk over driving the headphones and killing the sound quality (and possibly damage the headphone speakers).
If you insist on Bluetooth headphones, your only realistic option is to look for some with a higher wattage output. If you're unable to find anything that works, then you'll need to use wired headphones with a high wattage handling, then connect a headphone amp between them and the phone.
03-23-2019 01:42 PM