I asked that mag about measurements.
reply is :
"The measurements for max current are done with a single pulse 10 k signal, and ample recovery time after each pulse, so it is a true max current measurement. Pos and neg stand for the positive and negative half cycle of the single 10k pulse."
So Diablo300 is 1750W into 1 ohm , with peak current 238A/268A.
Pass labs INT250 is 280W into 1 ohm and with peak current surprisingly
low and also asymmetrical 21/31A.
Luxman 509X is 204W into 1 ohm and with peak current 104/107A.