Michelzay:
In most of the research I did before purchasing the GCPH, I found no sources that really found the sound quality unpleasant or unsatisfactory. Noise/hum were common complaints in earlier reviews, but never sound quality. I am still in the process of building my phono setup, so I have no direct audio performance to report other than the noise issues mentioned above.
I do find it strange that the GCPH in your system sounds good when connected directly to your power amp, but not to the same power amp thru the MAC line amp (pre-amp). That would indicate to me that there is an issue with the line stages in the Mac pre-amp, either a voltage overload issue or maybe an impedance issue (as you suggest). I doubt if it's cables, as I would assume you use the same cables to connect to the power amp. I am also assuming the power amp has similar impedance/voltage requirements as the Mac pre-amp.
I would try backing off the gain in the GCPH and see if that does not improve things. Also, try different Aux line inputs if they are available. I know my Parasound P3 had different quality amplifiers connected to the different inputs. Maybe that's the case with yours as well. If not, maybe you need to move on to another product.
In most of the research I did before purchasing the GCPH, I found no sources that really found the sound quality unpleasant or unsatisfactory. Noise/hum were common complaints in earlier reviews, but never sound quality. I am still in the process of building my phono setup, so I have no direct audio performance to report other than the noise issues mentioned above.
I do find it strange that the GCPH in your system sounds good when connected directly to your power amp, but not to the same power amp thru the MAC line amp (pre-amp). That would indicate to me that there is an issue with the line stages in the Mac pre-amp, either a voltage overload issue or maybe an impedance issue (as you suggest). I doubt if it's cables, as I would assume you use the same cables to connect to the power amp. I am also assuming the power amp has similar impedance/voltage requirements as the Mac pre-amp.
I would try backing off the gain in the GCPH and see if that does not improve things. Also, try different Aux line inputs if they are available. I know my Parasound P3 had different quality amplifiers connected to the different inputs. Maybe that's the case with yours as well. If not, maybe you need to move on to another product.