Both are equally important but if you are not planning to replace the good one with a better one, then I would suggest to use the better one for DAC to pre, because it carries low fidelity signals than the preout which applies gain on the signals. In other words, the output from DAC is more sensitive and susceptible to distortions. I have no research done, this is just my understanding. We will wait for experts to comment.
But why don't you test it yourself and give your feedback for all of us.
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