@audiokinesis,
This post may read a bit differently from some of the above thread. If your wooden countertop is situated along the 18 ft. wall, then your situation may not be nearly so dire.
If you can get say, 8-12 ft. of centered speaker separation and move your 13 ft listening position a bit closer, you may be okay.
Speaker selection and positioning will be key. Speaker plane should be positioned at or slightly beyond the edge of the cabinet. Flexibility for at least some tow-in will help.
Importantly, you should avoid using any open port rear-firing speakers. Unfortunately, this may rule out your otherwise excellent choice of the KEF R3. However, a baffled rear port will allow close-wall placement.
I can speak to you with some confidence because my room is very similar, and over the course of time I’ve tried most permutations. With some effort, You can set up a very effective near- and mid- field listening experience. Try to think of your room as say, 18 x 20, just without a back wall. Listening in the back section may not be highly resolved stereo, but you can still rock out to good hifi sounds.
As for components, in lieu of my first wish to suggest Ayre Acoustics EX-8 2.0, ($8000) I think I instead have another strong recommendation for you to consider:
Buchardt Audio S400 Mark II speakers ($2100), (amazing speakers, good for near wall) and
Buchardt Audio I150 all-in-one integrated amplifier ($2000) minus $500 if bought with the speakers. Check out the specifications and great reviews.
Buchardt will ship you the components to try out for 4 weeks. 100 bucks no hassle return. Then, for around $5k, some cables and possibly a sub or two, you might just be well on your way. Good Luck!