I would say the minimum required to get the new speakers is to get a stereo amplifier (or two mono). Leave everything as is except that you plug cables from the pre-amp of your receiver to the external amplifier and plug the LFR on the external amplifier.
I don't know, I think the minimum needed is four channels of external amplification for a pair of LFRs.
The left and right pre-outs go into the DSP box, and that provides outputs for the left-front, left-rear, right-front, and right-rear drivers. Each of those arrays needs their own amp channel.