Balanced Streamer/DAC to Unbalanced Preamp

Check the specs on the Lumin D2 and make sure the output impedance is the same from the XLR and RCA outs. If there is a difference then that could mean using the RCA outs limit the DAC’s potential.  

Nope!

Thanks all. It's what I thought but great to be able to get some quick advice here!

The only time I had to convert was when I was trying to use single-ended tubed preamps into a pair of large solid state monoblocks that only accepted balanced inputs.  The best way to do that was through a pair of transformers such as the Jensen ISO-MAX products or  those made by Lundahl.  I used Jensen, but with either you need to check the impedance matching since the transformers are sensitive to a narrower range of input/output impedances before rolling off frequencies.

As the others said, just use the RCA connections.

No 

Yes

As others have said, just use the RCA connection. If you ever get a pre with balanced input, you can try using balanced and see if it is an improvement to your ears. (Even if not, you might find, as I do, that XLR connectors are better designed and less likely to come unplugged or cause hum.)

nope

Nothing to be gained unless both are balanced, just use RCA