My exotic and expensive Schiit preamp (cost nearly a thousand dollars!) has a "passive" setting so you can instantly hear it not doing much. I know it's expensive but totally worth it...
No preamp in system
I want to point out how the perception of our equipment changes over time. I’m getting so use to the sound of my system without a preamp (which is out for repair) to the point that I’m accepting it as good sound. It reveals something about our hobby. When we get new equipment we often say “let it break in.” And lo and behold, it sounds much better over time. Is it that were really fooling ourselves, and that it’s simply a matter of us getting use to it?
Just food for thought.