Which DAC as a preamp?

I owned sources who has a pre amp inside.

All should get out of the habit of saying this. It should be "I have a source with digital domain volume control"

As "most" sources that have volume controls done in the digital domain DO NOT have preamps in them, they have standard low impedance output buffers. No preamplifiers!

Only if the specs of the source say that it can output more than say 6v to say 20v can you say it has a preamp which pre amplifies.

If it’s below 6v then it’s just a dac/cdp that happens to have a digital domain volume control with output buffer with or without some small amount of gain, to bring it up to Redbook standard of 2v some kick it a little higher 3 or 4v.

Cheers George

10 years ago I bought a Pass Labs XP-20 pre amp. After that I used my Meridian 800Daxv4 with inbuild volume control for a pre amp for many years. 

By adding a good pre amp you will hear the benefit of it directly. The precision of a pre amp is bigger than you can imagine. It gives both voices and instruments much more a shape. Beside that it creates better dynamics as well compared ot a Dac with an inbuild pre amp/volume control.

You need to learn people and also let them hear the differences by using a real pre amp. When you did not hear/audition it in a comparison it is not possible to understand it. There is still a lot unknown in the world of audio.

From someone who’s actually been designing preamp/amps for almost half a century instead of just reading the specs. 

https://m.youtube.com/watch?v=HHl8F9amyY4

Thanks for all the input folks. I ended up with a good deal on a nice peach tree sonadac. Small form factor like the amps...triggers them by remote....running balanced cables...sounds great. I am breaking the amps in, but so far I am VERY impressed with the red dragon amps as well. This may be my favorite system of all time!