Who is using their DAC as a preamp?

For late night listening, I currently have a Schiit EQ (Loki) in the effects/tape loop connection of the Rogue. I just boost the lower frequencies a little...basically I use it as a loudness switch. Since the EQ has "true" bypass, I can just use it in line between dac and amp if I decide to ditch preamp.

An excellent choice for late night low volume listening, and the Schiit Loki at $149 is a bargain, does all what you said and more,   https://www.schiit.com/products/loki   just put it between any of these configurations: 
1: Between source and poweramp (if you have source volume control)
2: Between source and preamp
3: Between your preamp and poweramp.
4: Or in the tape loop on an integrated amp.

Cheers George 

There is a poster on another thread that uses a 1/3rd octave 31 band eq, as his passive device ( it has dual channel gain controls ). He compared it, flat, to 5 K preamps, and says it is superior to his ears. I have the same eq ( and I tried it via his recommendation ), but did not feel it came close to my Luminous unit in sq. However, it bettered some of my cheapie preamps ( RGR, Hitachi, AGI, Citation, GAS, SAE, Dynaco ). I sold my 2 megabuck preamps, which were both bettered by my Luminous unit.

I have been learning a lot about volume controls of late. In my years of having various components, I have never really thought about volume control quality. 

Back to the Mytek. Darko has a review up with a preference of an outboard preamp (BHK Pre-$6000). Darko does state, however,  the Mytek does sound very good job with direct input

Cleaner than the Sys...Ebay item # 253818627052...HiFi version. $40 or less, shipped. About what you would pay to build one. Promise..

It is the only way to go. There is so much fun digital stuff like room control and digital bass management. I send my phono amp to my digital preamp/DAC through a Benchmark ADC. The analog guys are now vomiting. But very few of them have heard digital room control and bass management work. The Best unit out now is the Trinnov Amethyst. The one I use now is a Tact 2.2X. Tact is now defunct but the 2.2X is a jewel. You just have to understand it's idiosyncrasies. Boy does it ever work great.