Weak link

weak link 1 = lack of subwoofers

Get a Elac Varro DS1000 and use the built-in calibration tool it comes with (very handy tool for all subwoofer noobs). 

weak link 2 = lack of power conditioner

Get a Niagara 3000 or 5000

+1 @knotscott I would spend some effort treating the room.  You have very nice components.  Room treatment is likely the best bang for the buck.  A pair of subs would be interesting as well.

To refrain others, without a budget, photographs, and a room description/dimensions it’s hard to make recommendation on your solid system.  I would address the following, in the order listed, for both will have a positive effect on SQ:

1:  Power quality.  A good conditioner like a Shunyata Denali or Everest, or an Audience Adept Response T series.  Then, if your home design permits without much construction cost, dedicated 20 amp power lines.  If possible, one for digital and one for amplification.  
2:  Room Treatment. 

That’s a great system. +1 for dedicated lines. If you are technically inclined get a usb mic and fiddle with REW to see how your room rates. Then look at room treatment. I have tried and like the WireWorld Eclipse interconnects, but you might try some other ones. I found them a touch on the dark side. I have not tried the ww speaker cables, but worth some research if you are on the lower end of their lines. 

Your room is the most important component of your system. If it’s not treated, you will be fighting to get th best out of your other components.

You didn’t say what you didn’t like about the sound you are getting. If you don’t like the bass, room treatments will help. If your don’t like the soundstage/imaging, room treatments will help.

I would hold off on buying any subs until you treat your room. Your speakers are sized appropriately to your room size so you might not need subs. My new house has abut the same size room as yours, and when I bought new speakers sized for my room, I pulled 1/2 of my room treatments out of my room that were used because the other speakers were too big for the room. I have subs but I don’t need them with the new speakers. I still use corner tube traps and 1st reflection panels.