No, no.....

Let me re-phrase. I know that you have a 2 Ohm load composed of two 4 Ohm loads.

However, the original spec you quoted just stated the power at peak, and RMS, that the amp delivered. These figures are meaningless unless they also specify the load they are designed to deliver to.

Since you have a 2 Ohm load, and each part of the load is only getting half the power, then that's correct: it implies the amp is designed to deliver 390W RMS into 2 Ohm. No problem there. But that's Ohm's law, so if you now attach just one sub (4 Ohm) you will only get the amp to produce half it's rated output, which is the sub's rated power.

I am no longer sure what you are asking for here, to be honest!