Are Pre-Amps necessary?

You already answered your own question. The rest are just someone else's opinions. 

Yes, unless you dedicate yourself to researching and investigating really compatible components… I mean way harder than just high end audio… or you simple love the sound of one companies products together. Then the answer is a good preamp is the heart of a great system. Many people have tried, many people have given up. 

By the way in general, tone controls don’t perform the function to which they are designed, note high end audio equipment do not have them, and digital processing has basically the same problem. You want equipment that does a very minimum very very well and nothing else. Low end equipment comes with all sorts of buttons and functions.

I am sure some day great preampless systems will common… but honestly not for a long time.

Yes

Never heard a pre that "Improved" the SQ compared to "No Pre".

@vanson1 My Benchmark HPA4  preamp improved the sound of my Benchmark DAC3 HGC. This DAC has a volume control for DAC direct to amp. The preamp improved on the DAC direct to amp on low level volume listening. I used to do a lot of that late at night when the baby was sleeping.  You could hear all of the music at low volume with the preamp. Without the preamp there was music missing at the low volume. A rather frustrating listen. 

I have another preamp that is very interesting for those that want a straight wire with gain. It is the Topping pre90 for about $700. Unfortunately it is incompatible with my current office amp but if it matched I would keep it and sell a 10x more expensive preamp. The only amp that I got it to match was the Benchmark AHB2 amp. However, other people have had more success than me matching amps to that preamp. So if you have a lot of sources, for relatively low cost, you can try this invisible preamp to see if a preamp makes a positive difference. 

I have Room Correction via ROON Core Convolution files. No need for that in a preamp with a fixed and weak processor. So I have s computer to do the number crunching for DSP. I am not using DSP at the moment but it served me well in the past.