How important is a preamp for purely digital sources?

I've asked the same question and came to this conclusion - 
1) Is it necessary?  No.
2) Will it help improve SQ?  Very likely, assuming you pick the right one, which will involve time and money.  But it might not.
3) Most importantly, is is the best next improvement for my system?  Depends on what you're hearing and want you want to improve.  

Lots of good input based on others experiences, which can be helpful, but I think OP needs to share more specifically what their goals are to get the most valuable feedback.  

When I asked "what would a preamp do for me?" my conclusion based on forum feedback and my own research was to work on room treatments, isolation, power, and upgrade my source.

When I asked if upgrading my DAC was a good next step, my conclusion based on forum feedback and my own research was to work on power, consider different speakers, or to rebuild the XOs.  

This can be a strange and enlightening hobby, it's not all about buying a new black box.

I find a system sounds better with a
Preamp if you are going digital 
look into R2R Ladder Dac 
with a Jays Transport 

Well, oddly [to me, anyway], no one mentioned this, so I will ~ as observed, w/o a preamp, things do often sound a bit harsh...so I use one w/an added feature: EQ. Several spoke of the preamp "adding something"...why not be more selective about what ~ and where, in the frequency range ~ you are adding? Or subtracting, when necessary...My C48 has 5 band EQ, which allows me to adjust for my room acoustics and system synergy...the only way I would ever relinquish it would be for a c52, which has 8 bands of EQ, rather than 5.  Purists, please don’t bother ~I don’t have a perfect anechoic chamber for a listening room, and if you want to be stuck w/whatever sound comes out, and that sounds good to your ears, great...I’ve done some room treatments, which help out, but it’s basically a crap-shoot and it is SO much easier, faster, and less expensive to make a slight adjustment to a few dials...and this way [unlike w/digital room correction], I can tweak to my room/speaker response/ears.  And, I’m using a Berkeley DAC, so I really don’t think I need EQ because my DAC is so poor...As a final observation, I find it interesting [and refreshing] that some of the writers of TAS, Stereo Review, and others are now swinging around the other way, and are openly in favor of a judicious use of EQ to enjoy their music, rather than viewing it as some anathema of evil to be avoided at all costs...try it, you might like it ;-)

Apparently rather important ...
  https://forum.audiogon.com/discussions/simply-amazing-coda-technologies-07x-preamplifier

I haven't used an active preamplifier since 2010, and I don't miss it, figuring that adding unnecessary circuitry to the signal path can only degrade the sound, especially if there's capacitors and op amps. I have a Luminous Audio Axiom 2 (a passive that costs $195). You get to remove  potentiometer from your signal path completely that way: the pot is shunted to ground, and a foil resistor is in the signal path. I found some of the responses amusing; about how people think their expensive preamplifiers add "depth of the soundstage", "clarity", "musicality", and "micro to macro dynamics". The DAC outputs are at the Redbook voltage level, and the signal doesn't need to be boosted any further before it gets fed into a power amplifier. There's usually two op amps in the output stage to convert current to voltage.