Receiver Too Weak?

You can boost the center channel (where dialogue lives) to make it more easily heard. Run it into a ribbon tweeter to make it easier to understand.

A simple compander adjusts the dynamic range to your liking.

EasyTarget, most receivers have the ability to control the volume of each channel.  I suggest bumping up the center volume to help you hear dialog, but keep the front R L channel volume the same, so the loud parts of the show don't get too loud.  I find the really loud parts are mostly the R&L channels.  

As to lackluster sound, as GHD said, your receiver does not have power (current) to dynamically drive your R&L channels to their full potential.  And the overall quality of the processing and output of the receiver will limit performance.  

Not all of the issue is the AVR, some of it is the sound engineering on the movie. I run into this a lot. Some movies have a perfect balance between speech and sound, others do not. 
I have a Denon that is supposed to be their "best" AVR for sound (it sounds not-great, but not terrible with music). It has a buttons on the remote to change between movie, game, etc, and when you press a button it brings up a menu so you can choose between different type of Dolby and other interpreters. I just try to use those to get a sound that works for each film, and if that fails there is another button that lets me boost the center.

The last thing is what others have been saying, your amp may not be up to the task of driving your speakers. In my case, my AVR has a line out that I run to my preamp and direct to my monoblocks. The limiting factor of an AVR's output is the power supply, if you look closely at the power ratings of your AVR, you will see it goes down the more speakers you add, de-rate their claimed output by 30% to 50% and you will be in the right ball park. I would suggest no less than 150 watts per channel with all 5 (or 7) channels being driven for those speakers if you want good "life" in your movies.

I frequently prefer forcing '2 channel stereo' setting rather than the default surround a lot of programming defaults to.

you can also try 'direct'.

On second thought, yamaha receivers do offer some features like dialog level, dialog lift (if your center channel has suboptimal placement), etc after you get into their Aventage line. Hence, the minimum you should get is the Yamaha RX-A4A Aventage model. Such receivers have a bigger power supply and current to spare for your B&Ws. If it was still inadequate, it will have preouts for external power amps depending on the number of channels you’re running...it may even turn into ’hifi’ hometheater depending on the amp and power conditioning you chose.

Also, bump your center channel level a few dB up, as someone else suggested (and as needed). Set the cal mic right at ear height on a tripod. 

On a general note, if you have your center channel laying on the floor or stuffed in a cabinet, etc, it is not a good idea. It is also a good idea to have 3-way concentric driver designed speakers with a lower woofer/midrange crossover for center channel applications.