However, if you switch to line input you will need to provide power, but you will be much happier with the sound. These are bouth analog inputs.
So mics > battery box > line in, for example, is that right? Are these (mic in, line in) two different, physically distinct inputs on the recording device?
Why is the line in better than mic in? Because the mics pick up a better, fuller signal?
And what is the "digital line in"? What kind of input is that, how does it differ from an input from, say, a battery box?
here's a few more answers for you.
"Line-in" and "mic-in" are both analog.
"Digi-in", "Digital Line-in", "optical", "dig-coax", "S/PDIF" are all digital in. S/PDIF is a format to send digital information development by Sony and Phillips. This digital signal can be sent via a wire (coaxial cable) or via an optical cable.
on some recorders, the "mic-in" and the "line-in" share the same physical input jack. For example, on the Sony D8 DAT recorder, the mic-in and line-in are both via the same 1/8" jack, and there is a switch that let's you choose between mic and line-in. on other units, sometimes the mic-in is via XLR jacks, and line-in is via RCA jacks. so that depends on the unit.
generally, it is "better" to run line-in, because people don't like the way the pre-amp in the D8 sounds. it overloads easily, and is not very "clean". So, if you use an external pre-amp and run line-in, you can bypass the crappy internal preamp in the D8. You can buy very high quality outboard preamps, and these are generally better than the preamps contained within the recorder device.
The reason why digital-in is "better" is the same logic. If you are recording digitally, the signal must be converted from the analog realm > digital signal at some point before the data is recorded. generally speaking, an outboard A/D converter will be of higher quality than the internal A/D converter within the recording deck. i.e. if you have a very high quality A/D converter, and then send the digital signal to the recorder and the only thing the recorder is used for is to write the data. if you go analog into the recorder, you are relying on the A/D converter of the recording, which generally speaking, is not as good.
However, it is important to rely on what you think is "good." This is all just general info. the internal pre-amps and A/D converters in some decks are better than others. For example, if you have a Sony D100 or m1, you might be happy with the internal A/D converter, and then there is no need for you to get an external A/D converter. If you have a new Sound Devices 722, chances are, you could be very happy with both the internal preamp and the internal A/D converter. and then run your mics straight into it. or you might like the sound of a Lunatec V3 better, and choose to run digi-in from the V3.