The latter statement is absolutely true: if nothing is there then no amount of enhancement will bring anything out.
The earlier statement is very much an it depends kind of thing. Increasing volume, either master or just specific frequency ranges, doesn't make things clearer or more detailed per se. What it can do is make those details more readily perceptible. This is especially true for the higher ranges as humans tend to lose high-frequency sensitivity as we age. Thus, increasing treble volume can make the treble range sound more clear and detailed.
Indeed. I wasn't meaning to imply that details magically form out of thin air. Not even firmware 1.2.2 that people have been claiming is highly detailed can do that. Just increasing the volumes of the frequencies that contain the details, will allow one to hear them better, if they are there to be heard.
Bass detail however is different, and generally boosting the bass reduces its detail being counter productive. Also highly dependent on the headphones ability to stay clear, without drowning everything out. In my case, my current headphones are rather bass heavy. While I do like bass, I don't like excessive amounts of it. Not only am I getting a perceived increase in audible details by boosted the high frequencies, but I gain an increase in the clarity of the bass, such as the vibrating strings of a cello. In that case, the bass details may be there, but the chosen headphones can destroy them. However electronic bass I don't think has any details in it, as such these genres can be great with some excessive bass.