The most sensible way to get these together would be to remove the amps from the Pentas (easy, as what will be left will be a pair of passive Pentas with now useless display modules inside).
You could probably also attach the Speakerlink inputs of the Pentas to the 4400 outputs, or use attenuated phono speaker adapters connected to the line inputs on the Pentas, so you will using the Penta amps (with no displays).
The latter methods will be a terrible waste of both the Pentas and the 4400, the first method a terrible waste of the Pentas