The Best Preamp is no Preamp?

exactly, a good pre-amp in the chain always seems to work better.

from my personal experience, DAC direct to Amp sound flat and sometimes the bass just sounds even worse.

Recently, i tested going from my Lampi Pacific direct to my 300B mono amps.  I was shocked at how good it sounded.  Maybe it is system-dependent but in my case with 98db horn speakers and having 16 Wesstern Electric 300 B tubes in my amps, I don't need a brain.  

I have to agree a great preamp will change and reveal what your system should sound like with the magic quality,  compared to just playing music nicely. I ran a parasound preamp( holo no real  sound was stale, dead sounding), then ran balanced xlr from balanced dac smsl to a old but nice anthem reciever amp( cheap way to get great volume control but no real magic to the sound but nice for cheap).

Then ran a conrad Johnson pv11 with tubes but no xlrs, opened stage, could hear separation better but not coherent, was happier but still missing something. Then bought audio research ls17, omg wow drop your jaw. This was use as reference for reviewers 10 years ago and I know why. 4k or 5k new. Run fully balanced smsl to audio research ls17 out to jeff rowland class a amp to 1.6r Maggie's.  Wow the sound went holographic, live sounds amazing, can hear all instruments  in sound stage but sounded musical, and bass tightened up so much and hit harder, so it's a journey but preamps can take, control, and pull everything  together to sound amazing.

You could go with just a control amplifier. 

Using an AVR for pre amp, says enough!