Value of a preamp?

Depends on your DAC! If you get the new Lampizator Poseidon, it does not need a preamp, because the impedance level matches any amp. 
same with playback designs.

fwiw, i just did a listening session with a naim power amp and a ps audio 5.0 preamp, which has both an active and passive (straightwire) mode. at the same volume, the active mode had significantly deeper (but less sculpted) bass and more dynamic slam, while the passive had less overall oomph but a lot more high-end detail and, predictably, a lot less coloration. we all preferred the passive, except for vinyl, which sounded a little flat. of course, i'd expect impressions with different gear.

Would not touch any Limpazator products with a 10 foot pole. Nothing but problems. I am normally very impressed with EU gear. 
 

Depends on your DAC! If you get the new Lampizator Poseidon, it does not need a preamp, because the impedance level matches any amp. 
same with playback designs.

I don't understand the question.

For people going straight from their DAC to amplifier, you don't know what you're missing. It's been a huge difference for me in several iterations of my systems through the years.