A few other things to consider: try using a monaural signal path
utilizing a single loudspeaker for auditioning the final material. The
complex phase relationships that occur when using stereo equipment
(especially two speakers) can be the cause of some serious errors.
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To my ears there is a vast difference between two speakers and one speaker for monaural listening. 78s were all monaural and practically all listening was with a single sound source. Putting the 78 sound through two sound ports changes the medium.
Unfortunately hardly anyone will listen to the restored sound through a single channel. So what do you want your monitor to show: the sound of the 78 or the sound people will hear?
Mike Csontos