Equalizers and other processors were, and sometimes still are, generally inserted into tape loops, which places them "before" the volume control. In some situations it might also be appropriate to insert a processor between preamp and power amp, or in the case of an integrated amplifier between the output of the preamp section and the input of the power amp section. That of course would put the processor "after" the volume control.
So the line would go from cartridge to aux input to line preamp out to MM phono preamp in to mm phono preamp out to line preamp in.
If the MM phono preamp is inserted into a tape loop of the other preamp, as I indicated earlier preamps often do not provide much if any gain between their line-level inputs and their tape outputs.
If the main output of the first preamp is connected into the MM input of the second preamp, then as you now appear to realize the output of the second preamp would have to go to the power amp, not back to the first preamp.
That arrangement would function, but it would also create the risks and sonic issues that I described in my first post above. As well as the loading issue that Armstrod pointed out.
The same cumulative gain could be realized, without most or all of the risks that I described, by simply connecting the turntable into the MM phono stage, connecting the output of that preamp into a line-level input of the other preamp, and connecting the output of that preamp into the power amp. The result, though, would probably be totally unacceptable hiss levels, because chances are that the signal-to-noise ratio of the MM phono stage would be inadequate for LOMC's.
Onhwy61, thanks for the nomination!