greensparrow, when you connect the kind of microphone you have, you would use the mike input, not the line input. Since you asked: The line input is affected by the record level control, just as the mike input is, provided that you have the "REC MODE" switch set to "MANUAL" (which means "the user, not the recorder, is responsible for setting the recording levels").
But the mike input is also affected by the setting of the "MIC SENS" switch that's immediately to the right of the mike socket. If the switch is set to "L" and you can't get enough level on the meters, try setting the switch to "H" instead.
Note that the meters on the TCD-D8 are driven by its analog circuitry, and they aren't completely precise in responding to brief signal peaks. If you see the "OVER" indicators light up (which are driven by the digital circuitry and are precise), it's important to back off the levels a little, even if the meters aren't reaching 0 dB. I've seen situations where the meters showed levels of -5 but the "OVER" indicators came on.
If on the other (third?) hand you find yourself turning the record level control down to, say, 3-1/2 or below, then if you were using the "H" setting of the "MIC SENS" switch it's time to switch it to "L" and raise the record level control--because otherwise, you'll overload the inputs of the mike preamps in the recorder.
I hope this makes some sense--it's definitely a little confusing at first.
--best regards