Excellent observation on speaker efficiency.FWIW, verify the efficiency between the center channel and the front pair.
I had that issue running a JBL Stadium "voice" in the Center, and 2 2x 8" Klipsch "Icon" towers. I had to leave the TV speakers on to hear the center. I got fed up, and bought a Klipsch RP-250 C center, and the problem went away. Klipsch is claiming about 98 DB @1 watt on the towers and 96 DB on the center. The JBL center was something on the order of 89 DB. So, more than double the volume from the Klipsch center.
Other than that, I usually kick on the stereo when late night TV hosts a live musical act. I think the sound engineers might be mixing the front person toward the back on purpose, since half of them can't sing. Not to mention the lyrics are mostly worthless, repetitive crap anyway.
I'm AV geeky enough that I have several 5.1 setups throughout the house, and boost the center even when it's an exact match as part of a 5.1 package. The only exception is on my main PC where I dropped the center level, but the speaker is on the desk right in front of me and I don't really watch movies/TV on it.