PT2257 only gives me heavy buzzing sound
many amps and BT audio chips use differential input/outputs. none of the inputs nor outputs are considered grounds.
the Lp(left,postivie) Ln, Rp and Rn on your audio chip should be connected to loads directly. Ln or Rn are not audio grounds. so you can't use simple POT volume controls or any processor or amplifier chip that doesn't support differential IOs. so, you can't use PT2257 in this circuit.
for better understanding here are two audio signal types:

the simple, well known one, which consists of GND and an audio IN per channel. you can use many amplifiers, processors (e.h. PT2257) and POT volume controls. and one end of the output (e.g. speaker) is connected to GND.
the differntial audio signal which consists of a GND and a pair of IN+,IN- per channel. you can't use the soulutions mentioned above. for example, if you wanted to amplify the output signal of the bluetooth chip, you have to use something like PAM8302, 2.5W mono class D audio amp per channel. note the IOs: