Just to avoid confusion, my understanding is that water debit is how much water is pumped out in a given time with no resistance (ie. coffee) and is important for diagnosing pump issues. Youre looking for ballpark 100mL in 10 seconds.
I think that if you program the volumetrics to do a double shot, youre looking for 75mL or so, which should give you 60mL in the cup with the rest absorbed in the double puck. Should be the same volume regardless of how many groups your machine has. If you set it without coffee in place, the water should come out way faster than the time for an espresso, though ...
I hope that helps ... or have I just confused us both?!