Platsolos, first try to be 100% sure that the DX 51 DAC is the same that goes into the TL51ZMKII that I have.
The shop guy said yes, but when looking at the price it seems not (a DX 51 is much more expensive of how it is valued inside the TL 51ZMKII)
Maybe they are making a special price package like sometimes happen and naturally they save on the enclosure cost.
If we can determine this I can be of help as I can compare it for you with other converters that I can listen in comparison.