The question is if the preamp stage that is built into the Lumin is better or worse than an external preamp?
Doesn’t matter, as the Lumin’s "preamp" (output stage) is still in the signal path, there is no bypassing it.
Why run one preamp into another, series’ing up all the distortions, the last one doesn’t get rid of the first ones, they just accumulate.
Cheers George