I'm a big fan of doing things wired. You can certainly go through the hassle of bringing a speaker in/out whenever you want to use it. But, that's just it. It is something else to store in your home, something else that must be charged and ready to go when you want to use it. You will want a unit that can work when plugged in when you want to charge it up, and ensure it has enough power to run it when it gets low on battery. It's not the end of the world if this is something you are prepared to deal with on a regular basis.
Personally, I ran wires outside. It does suck a bit to run the wires, but once the wires are in place, they are there forever and speaker wiring technology really hasn't changed in decades. So, you are likely good for the life of your home if you run some 14 gauge wiring out to some speaker locations. It is ONLY painful once, bringing speakers outside all the time and charging them, etc. is painful every time you want to use them.
I have done outdoor rock speakers for some clients, I've done speakers on stakes, but in patio areas I typically use traditional outdoor speakers and I've found very little difference in audio quality from those speakers made by Outdoor Speaker Depot and many of the name brands for a lot more money. I typically put them under awnings and such to help keep them out of direct weather. I have also put them under wooden decks to hide them completely while getting a reasonably decent sound for the people above.
Other considerations:
Your existing Denon receiver, if you are currently using it in a 5.1 audio setup, allows you to connect the speakers directly to the assignable Surround Back speaker terminals to power the outdoor speakers. No additional amplifier is required.
Your existing Denon receiver offers streaming capabilities for many services which you can use for playback of audio outside.
Your existing Denon SHOULD HAVE a app which allows you to control it from your phone and adjust volume outside easily.
If using a different AV receiver, you just set the receiver up, following the manual, and choose 'NONE' for surround speakers, center channel, and subwoofer. It will automatically adjust itself to know that you only have left/right speakers setup in stereo.
When I go ride my bike in circles for an hour, I take a bluetooth boombox with me. It's not heavy, but not really light, but it gets the job done when I am only riding for an hour, and I only need to charge it once every few riding sessions. I don't play it all that loud. But, it's not something I would want out on my deck, and it isn't something I would want to forget about, as I'm pretty sure it isn't waterproof. But, I could see using a waterproof bluetooth portable speaker outside if I didn't have wiring in place. But, I would still eventually run a wire and I would strongly lean towards using zone 2 of my AV receiver if at all possible as that will give you solid streaming potential.