This question was discussed several times on EU but without any practical findings.
We have Track Level, Routing Vol, EQ Gain, Dyn Out Gain which are in digital domain and Master Volume which I believe is analog.
I experimented with one track of GND-SN/NS and one cycle 0dB 16/44.1 mono sine wave ROM machines to check if it is possible to introduce signal distortion with these digital gain controls. I connected MD to USB audio interface and used crappy oscilloscope application (http://code.google.com/p/audiotools/) to see actual waveform. I was able to see distorted signal only after adding Dyn Out Gain.
With all gain control set to max there is still no digital distortion which means that they are operating under 0 db and there is no way, for instance, to add some gain to make UW sample louder. In other words, all uploaded samples should be normalised if you want to operate with maximum SNR levels.
I can also see flaws in this experiment: it is not clear at what level GND-SN/NS signal is generated or what is happening with 16 bit 0dB sample during upload or maybe I should use white noise sample.
I also understand that it is a pure theoretical discussion and I should make music instead
So, what is your way to use all these gain controls?