Hi Nath
This is Tamal trying to answer your question.
You have already discovered the root cause of the issue.
Bluetooth is a limited bandwidth technology when it comes to data transfer. When you transmit audio from PC, it transmits in stereo but as soon you put microphone in business then one channel is occupied by the Microphone & the other is used for audio out. The quality drops from hi quality to telephone quality. It is expected behavior for a Bluetooth Headset. For simultaneous use of HD audio in & out you need to use a headset that has its own transceiver (a small USB thingy or base transmit unit). Those are real good headphones for gaming as well use in broadcast environment. You can go wired if you want lag free performance.