Also, if running external preamps, give the Tascam DR2D a chance. It runs for about 4-5 hrs recording to all 4 channels, and is dirt cheap
How does one do this? Can you meter both the mic in and the line in at the same time? From the pictures on the Tascam site, it seems like the 4 channel mode is really for the built in microphones.
Push a button to switch back and forth from metering the line-input to the metering the mic-input. Mic input can be either the internal mics or the external mic-input jack.