The Best Preamp is no Preamp?

but is there any explanation for how putting a preamp in the signal path when you have a fairly higher-end DAC can make an improvement?

Yes. The explanation is offered earlier on this thread.

That’s the only real fun to be had in audio.  Trying something new is a very good thing as long as you don’t blow up your gear. Keeps things interesting anyway. I’ll try it sometime with my Node2i. 

Everybody talks about high quality preamps, which makes over-all sound good. Yes, the pre MAKES (modify) poor sound from poor sources to be good. That means the pre does change the original music signal into slightly different signal. The modified signal would be good to our ears. Do not praise the preamp that makes poor source better. Just blame the poor source. If you have good source (well-recorded CD for example), you can enjoy the music much better with no preamp. Why does tube-based gears make good sound? Just because the tubes tend to add some distortion to the original signal, and the added signal makes our ears pleasing. The added signal is usually even-order frequencies.

Shorter speaker cables make the over-all sound better? I have to laugh at the guy who says that. Inside the speakers, there are very long coils. Due to limited space condition, the coil's physical shape can not be better than that of speaker cables. Compromised long speaker voice coil and very short speaker cable? Usually, the speaker cable length does not matter very much unless the cables run longer than 50 feet.

Agreed!  Even gooder is eliminating power amps (technically).  Music server feeding Weiss 501 DAC/volume control directly to ATC active speakers.  Faster, more dynamic, more detail and only four pieces to reproduce music.