Good amplification is important for both, SQ and SPL. In SQ application the amplifier gives you good dynamic range. And for SPL.. again there is no substitute for even more amplification. Most speakers will perform best once you run 50-100watts to them. This is specially important for reproducing the lower frequencies since this is where most power consumption happens. However, I wouldn't spend too much effort on amping the rear speaker. If you want to get the same kind of sound that you used to have, it may be worth it to get just one woofer from the dealer. If you replace the rear speakers with a different brand, replace both woofers. Don't use speakers with coaxially mounted tweeters if you have separate tweeters (in the case, it makes sense to install components).