Admittedly I don't have the patience to read everything that has been posted in this thread and/or the other thread referred to above. But I'm aware of a great deal of confusion on this forum about mike and line inputs, and I want to make sure people understand a couple of basic points.
One point is that you can't tell ANYTHING by leaving a mike or line input unconnected and listening for noise. If anyone is worried about the fact that they hear hiss (perhaps even a lot of hiss) that way from a given preamp or recorder, please stop; that's no proof of anything. An unconnected input is being "driven" in effect to an extremely low voltage by an extremely high impedance, and high impedance signal sources (even virtual ones as in this case) are full of noise. A microphone has (or should have) a low output impedance which causes the input circuit to behave very differently.
The other point is that you should reasonably expect a mike input to SEEM to have more hiss than a line input simply because the function of the mike input is to amplify any incoming signals much more than the line input does. If you use the line input with the same signal source, you'll have to turn up the recording levels considerably--and that will only increase the noise. So again this situation seems to lead some people to highly confident but totally wrong conclusions.
To determine whether a line or mike input is noisy or quiet or in-between, you need two things. You need to know what levels (in terms of voltage) are typical for the output of your microphones when recording whatever you record; you also need a audio signal generator with low output impedance and adjustable level. (Note: If you're already saying to yourself that you can't make tests like this, fine--but that means that you truly don't know which inputs are how noisy. and anything you think or believe on the subject is only a guess.)
If the typical output levels of your microphones when recording loud music are, say, 40 mV then set the signal generator to put out 40 mV at some non-challenging frequency such as 400 Hz. Then feed that signal into the mike input of whatever preamp, mixer or recorder you're testing. Set the record levels (if it's a recorder) so that you get close to 0 dB with the signal coming in. Measure the signal coming out of the recorder at its headphone or line outputs, and/or set up a monitoring arrangement with headphones or loudspeakers so that the 400 Hz tone is as loud as the loudest sound you would normally expect to hear.
Now turn the signal generator off but leave it connected (remember, open inputs don't count), and measure and/or listen again. That's the noise floor to be concerned about. Repeat the experiment with the generator connected to the line input, and I'd be surprised if you can even turn things up far enough to get the meters to read near 0 dB--but even if you can do so, there's a very good chance that you'll find the line input to offer MORE noise rather than less, because of how far you have to crank the gain up.
--best regards