Some updates...
Actually, I am using LG HBS-730 rather than HBS-750 model, and I am having the same problem. I assume this type of "volume-control" problem applies to all models that LG bluetooth stereo headsets have released.
Below are the devices that I have tried with HBS-730 model...
Laptop:
MacBook Air 13' (released Summer 2013)
-> Works fine. I wish all the other iOS devices work like the MacBook devices.. Although I have not tried my LG
Smartphones:
Samsung Galaxy S3 with KitKat 4.4.2 version
-> Works fine. I wish my iPhone 6 works like my previous Galaxy S3 with LG headset!!!
iPhone 3GS with iOS 6.1.6 version
-> Too loud even with the lowest setting on the volume..
iPhone 4 with iOS 8.1 version
-> Too loud..
iPhone 5 with iOS 7.1.2 version
-> Too loud..
iPhone 6 with iOS 8.1 version
-> Too loud..
Tablet:
iPad Retina display with iOS 8.1 version
-> Too loud..
Sooooo... any iOS devices (iPhones and iPads) have an issue with volume control when using LG HBS-730. I believe same goes for HBS-750.
I wonder whether either LG or Apple will tackle this problem at all... 😟