that rating is for strapping a pair of amps together so a d2 would work fine if someone was strapping their amps together, steve is just running them all master slave so a d1 will work better for that setup you will see much higher than one most likely because you are using one big amp for all your subs when you use one amp for one sub or one amp for one coil the imp rise isnt as great. fyi the only way to figure out what you are actually rising to is to record amerage with a clamp and ac voltage with a dmm. there might be other ways but this is the only one i know of