By the way, the reason some people were putting BB in the chain is that a preamp at zero gain essentially is a battery box, providing power to the mics that helps them handle louder sounds.
There is already a preamp behind the mic-in jack--that defines "Mic-in." Line-in expects a powered or amplified signal, as from an external preamp. So if you were recording something really quiet, I guess you'd run mic-preamp-mic-in---amplifying the mic signal twice--but otherwise the preamp is for Line-in. And I find that with anything through a PA system, a battery box is all I need for Line-in.
For just about everything amplified, I run mics (usually CA-14 omni)--BB--Line-in to the PCM-M10. Volume is generally around 5-6. Your mics will probably have a different optimum volume level.
As noted above, neither a preamp or a battery box should make a recording bassy or color the sound appreciably in any way (unless they have a bass roll-off switch, which would lessen bass). The point is to amplify the mic signal to record it better--not to change it.