What am I missing? Pre/power gain and input sensitivity.

See, here's the thing about the internet: zero editorial standards.  Anyone can post anything. On this site your odds of being read are actually higher the greater the BS. Our #1 has 21k posts and when you ask if someone can find even one of value the question is removed and the 21k grows to 22k. 

So yes you are missing something: the necessity of DYODD. And no, you are not missing something. They are.

@millercarbon - You probably need to add more fish to your diet, buddy. You’re starting to blather again.

@cat_doorman, in the case of the example you cited you are not missing anything. The main effect of different preamp gains would simply be that the volume control would be set to different positions for a given SPL.

Preamp gain can often be a significant consideration, though, in the case of phono sources (or tuners, tape decks, and other sources which typically have much lower output voltages than CD players and DACs).

For example, using some typical numbers, if a phono stage provides 40 db of gain for MM cartridges and 60 db of gain for LOMC cartridges, and the cartridges are rated to produce 5 mv (MM) or 0.5 mv (LOMC) under the standard test conditions, in each of those cases the phono stage will output only 0.5 volts when a recording is causing the cartridge to provide its rated output (which corresponds to a volume that is quite high). If substantial additional gain is not provided by a preamp in that situation much of the power capability of many power amps will not be able to be utilized on many recordings, even with the volume control at max.

Regards,
-- Al