If you really want to impartially compare two audio products, there are two conditions that must be fulfilled, you really shouldn't know which component you are listening to ,so the comparison should be un-sighted.
The second is the outputs of both devices should be level-matched to within .1dB.
Your brain hears something louder and most always assumes louder equals better.
I would like to thank Serge Auckland for all of his technical assistance, he recommended a voltmeter with the correct range, which would be suitable for my purpose.
The meter used is a REK RVT-322 available for around £100 from Ebay. It is a dual channel unit which is useful,with a wide range of voltages/dB .
Methodology is to supply a steady state tone to the dacs being 'matched' Serge suggested 440Hz,I used the Sine wave generator application of REW software.
Macbook connected via USB to both dac units, measurements taken from pins 2 and 3 on the XLR outputs of both dacs, volume adjusted until both have the same output.
I am hopeful that Purité Audio can arrange a few level-matched and unsighted comparisons in the coming months.