My setup is to the extreme and I went for 7.1, and I reallllllllly hear a difference. I also have other speakers setup too, like for phone and for head phone, all which need amps.
Amp 1: 4 channel, for door speakers
Amp 2: 4 channel, for third row speakers, phone speaker, and center speaker
Amp 3: 1 channel, for Sub
Amp 4: 2 channel, for headphone jacks (6 jacks, one for each passenger).