In my opinion, the best way to go is one of the following scenarios.
#1
*One seperate class D subwoofer amplifer just for subs.
*Two 2-channel amps that are 2 ohm stable. Wire 4 speakers to one amp wired in a parallel configuration (2 ohm load). Wire the other 2 speakers to the the other (4 ohm load).
#2
One seperate class D subwoofer amplifer just for subs.
*One 4 channel amp. Wire up 4 speakers.
*One two channel amp. Wire up 2 speakers.