Pay attention on the measurement, to get the basic requirement first.
Like S/N ratio. Frequency response, FFT analysis, and channel seperation.
Comment on original setting.
Do you know the GAIN in the circuit when you apply OPA627?
I will attach a important application note about opamp at another thread.
You get the good sound but you did not have good S/N, i.e. some of the "original small signal" must not be presented.
