Technically, the BeePre II output impedance is "... 3K ohms at maximum ...",, i.e. no more than 3K (and usually less) - the text is not completely clear. In any case, that's not relevant when driving the 470K input impedance of the W-5M.
The maximum gain of BeePre II is 6dB (a factor of 2); Moreplay is 9dB (a factor of 2.
. The 3dB difference should be what you are hearing. It's not very much - maybe 2 or 3 clicks of the fine level control, certainly less than one click of the coarse level control. But the Moreplay does not (yet) have the stepped controls, so a fair comparison would be with the BeePre II coarse control at maximum.
The maximum output of the BeePre is 32 volts (if you drive it with 16 volts). It's often important to distinguish gain from maximum output voltage.
Hope that helps!