Balancing sound to sharpen dialogue?

That is called dynamic range. THX set the standard 105dB and since almost all movies are mastered to be played back like this and since nobody wants to hear dialog at 105dB it winds up being way down in the mix. You can hear it just fine with a fine rig, but pretty much everyone else is gonna be turning the volume up and down.   

Probably your speakers are back against a wall, that is both huge bass reinforcement as well as midrange muddling. Pull them out, toe them in, and soon as you are able please, please, please look into replacing the AVR. That one thing right there will muddle your dialog like you won't believe.

Dynamic range has nothing to do with it. Judging by what you are saying you have too much in the 200 to 300 Hz area and not enough between 3000 and 8000 Hz. The only accurate way to see what is going on is to measure the system with a calibrated microphone and matching computer program. But, you have to have some way to EQ the system,
like a DEQX unit. Bass is accentuated with speakers in corners and against the wall. Pulling them away from corners and the walls may help. Also check to make sure your tweeters are working. They blow easily. 
I have never watched a movie or TV show and had problems understanding the speech. Perhaps someone in your area has a calibrated mic? Where do you live?

Without having enough info of your speakers positioning i would suggest to move them a bit forward in the room and try to get them a bit closer together. From there you can listen if you want more toe in or not. 
As you do not have a sub and you receiver has basic eq features you can only play with speaker placement for getting a more enjoyable sound for both music and theatre. 

Thanks for the suggestions. I'll see if I can move them further from the wall, and closer to each other.

The Totems are really warm and have surprising bass depth, but when watching movies, dialogue never sounds as sharp as it should.

You’ve just got fat lower mids, which takes away from the diction of the speech.

Use the audio or bass/treble adjustment on the Onkyo and take the audio off movie and onto music/speech if it has it, or drop the bass a little with the EQ and this will bring up the "sharpness" of the speech.
Or bring the speakers well out from any walls, this also will fatten up the lower mids with excess bass
Cheers George