I believe its really important to know if the brightness is vinyl-only or vinyl and CDs. You need to figure this out first (as mijostyn stated).
Based upon my knowledge of the Zu Audio Souls M2, I don't think they are the cause, which is why I say check out how CDs sound. I have a hunch that it's your GCPH Phono Stage (I use to own one), but more information is really needed.
Based upon my knowledge of the Zu Audio Souls M2, I don't think they are the cause, which is why I say check out how CDs sound. I have a hunch that it's your GCPH Phono Stage (I use to own one), but more information is really needed.