Yes comparison to the SL would be interesting; I strongly suspect the SL would win, but not in ratio to the price difference!
In respect of providing ratiometric assessment of subjective differences, yes it's not an easy thing and very variable person to person, so individual opinions are of very limited value.
The only way to get truly reliable results is to use a large panel of people (>10), get them to undergo a set of calibration exercises first (using fixed comparison points) then repeat the assessment of the unknowns multiple times.
Far too much pfaf for HiFi, at least outside of dedicated companies like Naim!
I worked in market research for 12 years, mostly in the field of customer satisfaction. Quantitative research techniques are applied to the objective assessments of subjective topics as a matter of course and this provides reliable comparative assessments as long as certain statistical rules are obeyed, particularly the randomness, representivity and size of your sample.
Not sure any hifi manufacturer would be prepared to pay for the rather expensive quantitative research projects I used to run.
Geez, it has all come flooding back.
I have just realised I am again guilty of perpetuating thread diversion - apologies.
As punishment, I will report back on my findings from the home demo of the 555DR I have lined up.