Preamps opinion

I had a AudioResearch REF 5SE with a Pass x350 for many years, I found it a wonderful combination.

What you are experiencing to me sounds like a equipment problem. I would consult with an electronic repair facility. 

That should not be. These pieces are std audio. No insult here.  Are you using single ended input? there any chance your your DAC is plugged into the Home Theater max level inputs, instead of the ones marked analog?

What is your signal source? This has never happened to me. Sounds like an insufficient input signal. 

Unless you have a tremendous interest in emphases on detail at all cost, or excessive heavy bass (only like rock)... then the best Audio Research Preamp you can find. Ref 5 or 5SE... if you can. I have owned Audio Research preamps and prized their sound over different solid state (like Pass) and other tubed (McIntosh and CJ) for 35 of the last 50 years. Their sound has gotten better and better. Detailed, natural, midrange bloom, outstanding soundstage, great bass... I recently upgraded my REF 5SE to 6SE... but honestly they are in a class of there own. With the New REF 160s amp... my system really went to a new lever. Audio Research preamps have always had a magical sound to them.