I might have been misunderstanding your question. At the bottom I have what I wrote before.
If you are asking why you might like the volume not quite at 100 using the Leedh volume, that’s because something down stream sounds a little better with the volume down just a little. In fact many have discovered that they like the DS’s volume at about 92-94 instead of 100. (With releases before Windom, it was more like around 84 was the best.) So you might want to set the DS volume at, say, 94 and then see what volume you like best on the Lumin.
If indeed you were asking instead about changes in the bitstream caused by using or not using the Leedh volume:
When they disable the Leedh, they are truncating (or, more probably, dithering) the output to, say, 24 bits. The reason I asked is that the phrase “Bit Perfect” shouldn’t be used when talking about volume controls since they by definition deviate from no changes to the bits.
Since they assume that the DAC downstream can’t deal with more than 24 bits (or 32 bits) there is a difference in their box when using the Leedh vs. not. They can’t possibly simulate the DS’s volume because the path to any DAC is too narrow to hold the mathematically correct signal with a volume applied.