Any apps to boost the volume for bluetooth headsets?

The app that I use is called - Volume +. It works great and handled all types of volume settings including bluetooth, speakerphone, in-call. Works great, but, it's not free!!!!

https://play.google.com/store/apps/details?id=com.FREE.android.lvh&hl=en

 

O.K. you have to be rooted and it can be a little work to install but viper4android gets great reviews. I just installed it and I love it. You can set volumes for phone speaker, headset, Bluetooth, and usb dock. It has a built in EQ and many other audio settings for all of the above also.
Viper4android and more information than any one person can digest can be found here: [APP] Official ViPER4Android Audio Effects (… | Android Development and Hacking | XDA Forums

 

To be honest I only researched what I needed for my Galaxy S4. There are over 1000 pages of information in that link. I did say more information than any one person can digest! I know the audio driver you install depends on the processor you have but I think you can install the hifi version with any driver. You really need to just dive in and start reading. If you're looking for a "plug and play" app this might not be your best choice.
Wish I could be more help.
It would help if you completed your profile with your device and carrier.