Presuming you are using analog out of your sound card,
It is desirable to leave your MJ and Windows volume to 100% and change volume through an external preamp/receiver. The main reason for this is that volume control in windows or MJ is done by digital attentuation and is not very good quality.
This is a quote from my sound card manual (
Lynx L22 sound card manual), ON page 17,
"Volume Faders – Controls digital attenuation of the audio being played or monitored.
This control acts on the digital signals before D/A conversion. With the volume
fader at its maximum position, the vertical line within the fader turns black, no
volume calculation is performed and the audio stream is unaltered.
This is the
recommended position for critical recording and mixdown sessions in which
the highest signal quality is required. Volume control processing is done prior to
peak meter readings causing the peak meters to reflect any volume control changes.
Since volume changes act on the digitally converted signals, they have no effect
on the analog full-scale input and output levels. This must be done with the Trim
control. When the volume fader is not at its maximum or minimum position, the
vertical line within the fader turns red to indicate that the volume control is active."
The bolds are theirs, not mine.
Your sound card maybe different but windows volume control method is same and similar concerns apply.
Osho