If you calibrate all your speakers to have the same dB level using a Radio Shack SPL meter, or the built in mic setup on many new AVR's, you won't have issues. The Qs8's will handle more power and have better bass response due to the larger woofers, but the Qs4's are no slouch, they are great speakers.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85