@veerossi To add the phono section to the MP-3 is inexpensive if its ordered that way.
Regarding sound quality there are a number of variables. The most common thing you run into is that most of the balanced line equipment made for high end audio does not support the balanced standard even though it might really be balanced.
As best I can make out, the Lumin is an example; I say this because the balanced output has twice the voltage of the single-ended; if it supported the standard the voltage would be the same. One of the goals of the balanced line system is to eliminate ground loops and this is done by ignoring ground in the balanced connection insofar as the signal is concerned. The RCA connection does not ignore ground; when you see the voltage double what it usually means is that the RCA connection is one of the two XLR outputs (probably the non-inverted output, pin 2 of the XLR) and there is a second circuit that creates a single-ended inverted signal for pin 3 of the XLR. What's happening here is both signals reference ground.
The MP-3 doesn't do it that way. Its output, although direct coupled, acts very much like a simple line transformer with only 2 wires at its output- one tied to pin 2 of the XLR and the other to pin 3 with no connection to ground. So the advantage might be that the MP-3 can control the interconnect better, reducing artifact that the cable might otherwise have (and of course one of the advantages of that is you can run really long interconnects, allowing your speaker cables to be as short as possible; at home my amps sit on top of my speakers...). Of course if you have any other sources like a turntable or tuner then the advantages of a preamp are magnified. I use my DAC to accept HDMI for the home theater.