Your speakers have a relatively low efficiency, which is clearly giving your receivers a challenge. The combination of this low efficiency and the fact that speakers' impedances vary (dipping below their rated values regularly, such that a "4 ohm" speaker may appear as a 2.5 ohm load on occasion or an "8 ohm" speaker much actually present closer to a 6 ohm load at times) is probably responsible for most of the trouble you are experiencing. An amp like the M200 will have a much easier time with those speakers - unlike receivers (which typically don't like dealing with loads that are less than around 6 ohms), the M200 can handle prolonged 4 ohm (or lower) loads at high listening levels.

Putting a single M200 on the center would help during most TV and movie viewing, but your mains are apparently not much easier loads to drive, so you may still want separate amplification for them as well for two-channel music listening.