Tvad, you are correct, the input impedence for the DNA-125 is 100K, which wouldn't seem to cause an impedence mismatch. I must have been thinking of the DNA-500, which has a 10K input impedence.
However, the issue could be gain matching, as many tube preamps output a higher voltage than their SS counterparts. I also see that the DNA-125 requires only 1V input to drive full output, that's a relatively low sensitivity. By comparison, the DNA-500 requires 2.25 V for full output.
I could only find output voltage for the Dehavilland Ultraverve, which is 30V.
So a 30V maximum output from a preamp into a amp that only requires 1 volt input for full output could well be overloading the amp. Stick with SS preamps, many good ones have already been recommended.
Cheers,
John