Side-ways changes will not improve your system much at this point, but a dedicated surround amp for your speakers would be smart. I would look to surround-based separates for sources, as well as better cabling across your entire system. You should really be looking at Kal Rubinson's posts in Stereophile's website proper by searching for his column and his reviews on surround-sound. A great multi-channel DAC will get you much of the way home on sources, and you should be looking to improve your cabling, since you mentioned nothing... and I assume you are using the stock crap that came with your components. Those freebee cables suck like no other. Spend $50 at least on each cable in your system!

Your speakers are fine... all are in the same range of output. What you want to look at is the power ratings of your amplifiers into those speakers. Yes, a distribution box is pretty lossy and sounds poor, and will not transfer power adequately. It also brings down the impedance and power handling of your amp to handle your speakers... which means your amp is probably struggling to put out power.

Again, your amplification and cabling (Interconnect, speaker cable and power cabling) will be your most limiting components in your system.