Sorry I took so long to find your question. I was on a road trip and I'm not one of those people who take the internet with them.
Lets start by looking at some of the specs you state.
The 5 Hz to 60 kHz thing is not feasible and others have already pummeled you over this. But you admit that you are still learning and that is admirable. We are all still learning but some of us just don't want to admit it. "When we stop learning, we die" a wise man once said.
The range of human hearing is universally stated as 20 Hz to 20,000 Hz.(20 kHz.) However the range of acoustic sensation goes far below that. Perhaps you have heard of the "brown note" - 6 Hz - which is the most destructive to the human body. The Nazis (of course) built a brown note machine as a weapon. Luckily it was never deployed. It used gigantic horns on a flatbed truck driven by acetylene gas. It was massive and needed to be. The lower you go, the larger you need to be. It's common sense and simple physics. A very small speaker may be able to reproduce some low tones but not with any kind of volume. And volume is what is needed. It is a phenomenon of human hearing. It is less sensitive the lower you go. This is called the Fletcher / Munson equal loudness contour. All this means is that not only do you not want extremely low frequency performance but you need gigantic speakers to get it. Furthermore, there are only one or two instruments which can produce notes with fundamentals that low. Key word, "fundamental." A contrabasson can produce some really subterranean notes but they are all harmonics. They do not have that "ground tone" - the first harmonic - fundamental. The only instruments which can produce fundamental pitches below 20 Hz are the pipe organ and electronic instruments. These tones are perceived - felt more as shaking than musical tones. A really big orchestral big bass drum will also send out a shock wave that is in that region.
Above 20 kHz adds nothing. Most people can not hear much above 10 - 15kHz by the time they reach age 20. If you have supertweeters that go up to 30 kHz (and some do) you are only entertaining dogs.
Your receiver is old enough to qualify as a vintage piece. It has a silver face and that counts for something particularly when it is not silver painted plastic. Therefore, if I owned it, I would use vintage speakers with it. But lets back up a little. I have no idea where you got this receiver or what has been done to it. When I get a vintage piece like this I take off the cover before even turning it on and look for capacitors that are swelling. If I find any, I replace them. I also clean the potentiometers and switches with Caig DeoxyIt electronic component cleaner. I also do such things as power it up connected to measuring instruments and dummy loads. You just never know what will happen when you turn it on. That being said, I have no idea if you have already tested this receiver but you may want to consider having it looked at by a pro - for cleaning, if nothing else.
The speakers I'd use for a room that size would be something substantial with at least 10": woofers. Sansui made a lot of "big, hoinkin" speakers. Pioneer did too. JBL and Altec have become so collectible that their prices are out of reach by ordinary folks. RSL (rogers Sound Labs) made "JBL killer" speakers and the collectors still haven't inflated their prices.
However, it has been said almost ad-nauseam, that speakers need to be auditioned - listened to before buying. You can say that with just any piece of audio gear. But you can't do that mail order and the days when "stereo shops" existed are long gone. Best Buy is a joke as are the discount stores. But this is how people become collectors. They buy a set of speakers, don't care for them or think there ma be something better for their equipment and needs and buy another set. Thrift stores can be goldmines. Ive scored some nice vintage speakers at the Goodwill thrift shops but they invariably need work - rotted woofer surrounds and blown tweeters replaced with cheap radio Shack drivers are the norm.
But that's what I'd do if I were you;. I'd ignore specifications as far as frequency response goes - 40Hz to 15 kHz is perfectly adequate - and look at vintage speakers on eBay, fairly large, efficient ones.
You might also consider a kit from Parts Express, Madisound or Zalyrton. That way, if you don't like the sound, you can swap out drivers instead of the whole speaker - just like the first tinkerers did in the early Hi-Fi days.
That's something else you should look into - early Hi-Fi. It's fascinating how it all started back in the late 1940s and you seem to have "caught the bug" so you have something in common with those guys who wanted something more than the tinny sound of a Philco radio with a built in record player.