Tube DACs

For some time I've assumed that tube DACS are meant for direct output to power amps -- in other words, no reason to use a tube DAC if you are running through a tube preamp (unless all components are by same mfr and designed for synergy).

But lately I have seen posts implying some run Brand A tube DAC through brand B tube preamp -- say, Primal Luna 100 to Rogue RP-9. Can't find any prior threads addressing this topic directly.

So, question: am I wrong to suppose that pairing random tube DAC A with random tube preamp B is a bad, or at least a silly idea, absent a known synergy?
 

S