Just a minor correction to start - it's Aperion Audio - there's no "s" in their name
No biggie
First up, Aperion offers to pay the shipping BOTH ways if you don't like their speakers and want to return them. It really is a risk free trial. It's the absolute BEST kind of audition because you get to listen to the speakers in your room, not some dealer show room, and you get to use your own equipment. So if you are interested in Aperion speakers, go ahead and order some and try them out! If you don't like them, or if they don't work well with your receiver, you can send them back at ZERO cost to you. You don't pay any shipping either way and you get a full refund if you return them. You just have to contact them to tell them you want to return the speakers within 30 days. That's the only "catch". So no reason not to try them! Which is the point
Next, the Verus tower speakers - both the Verus Grand and the Verus Forte that you've mentioned - are nominal 6 ohm speakers with a
minimum impedance of 4 ohms. That means they are actually fairly easy to drive speakers. Your Onkyo TX-NR709 will have absolutely no trouble with them what-so-ever.
When you see the warnings about receivers having potential trouble powering "4 ohm" speakers, it's because a speaker that has a
nominal impedance (a rough sort of "average") of 4 ohms will often have dips down to 2 ohms or possibly even lower. And that can be a lower impedance than most receivers can handle. But a 6 ohm nominal with occassional dips to 4 ohms at just a few frequencies is nothing problematic for any decent receiver. So it's no problem!
The 90dB rating means that when you put just 1 Watt of power into the speakers, you will get 90dB of output from 1 meter (about 3 feet) away. This is on the higher side of normal speaker efficiency. Most speakers are somewhere around 86-89dB at 1 Watt/1 meter.
So basically, there's absolutely no reason for you to avoid the Aperion Verus Forte speakers. Your Onkyo TX-NR709 will power them just fine. They are quite efficient speakers that will play plenty loud without needing a ton of Watts to do so. And you can try them in your own home, with your own gear for 30 days with zero risk. Aperion pays the shipping BOTH ways.
So I'd say...give them a try! They're good speakers. I doubt you'll end up returning them anyway