Weak link

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.

1st, document what you are actually receiving at your ears, seated position

cd with test tones

Here’s one on eBay

Amazing Bytes CD with 29 1/3 octave Test Tones

Sound Pressure Meter, with bottom threaded hole for tripod mount

Meter on tripod, at seated ear height, at listening position.

Meter doesn’t need to be that precisely calibrated, you will get more or less answers relative to adjacent frequencies.

Make enlarged copies of the insert with test tone list so you can write down the results

Go forth informed

IF you have any tone controls, you can measure the results, and you can make adjustments for your personal taste, perhaps you have age related diminished hearing of high frequencies.

also, great tools to accurately measure the effect of alternate placement/toe-in.

room treatments are always good, but i agree with the get-a-sub--your kefs are great but i believe only go down to 35 or so.