The key determinant here is the quality of the analogue section of the DAC. Given its output, the only part needed is the attenuator of the pre if absent in the DAC. Often DAC attenuators operate in the digital domain thereby losing bits at lower volume. Should the DAC have a good attenuator with a high quality analogue section all a separate pre will do is add distortion.
Eliminated my preamp with amazing results
I pulled my preamp out completely. The result's were not subtle.
For those who stream music only... I was going from my laptop... to my DAC...to my preamp...to my amp. My preamps ONLY function was volume control. Source control not needed.
I started using Audirvana recently which comes with it's own high quality 64 bit volume control that was far better than the potentiometer in my preamp. It dawned on me that I could control volume using Audirvana and plug my DAC directly into the amp and bypass the preamp altogether. (Roon and Jriver also have excellent volume controllers) Note: Audirvana has an app download on a tablet/phone so it acts like a remote control. I'm loving it!
This not only eliminated the preamps volume control but it took out ALL the electronics associated in a preamp including some cables. A FAR more direct route. However, you must use caution and make sure the volume is controlled properly in the software since the amp will be fed wide open volume.
Having experimented with 'passive' preamps in the past (McCormack TLC-1) I thought the sound would possibly lose dynamics and bass response would suffer. WRONG!
The results were...Shocking!! Immediately the extended depth of the image was noticeably deeper. Background darker. The highs are the best I've ever heard. Pristine. The bass was dynamic, tight and most of all 'textured' in a way I never heard before. As I stated earlier the results are NOT subtle!
This is an experiment that took a few minutes to set up and yielded the best performance improvement of ANY other tweak I've ever tried. Not anything like using a passive preamp.
Equipment used... Peachtree DAC-itx.
Preamps...McCormack TLC-1 and Melos tube preamp.
Amp is McCormack DNA 0.5
Understand that different components will have different interactions with each other. Your results may vary. However, IF you don't like it, it takes just a few minutes to put the preamp back in the system. Nothing to lose and lot's to gain. After hearing this, I will NEVER go back to using a preamp.
Good luck!