need help with outdoor system

DLNA is a protocol that lets one media system talk to another wirelessly. Many receivers have it, . JRiver can connect to a DLNA server. However, I am not sure that a DLNA server on your receiver (if it has that capbility) can then deliver the audio to zone 2, which usually requires an analog input. Check the specs ouf

You can get a separate USB DAC to connect a laptop to the Denon. Something like the HRT Streamer II is less than $200, assuming you have a laptop to run Jriver in the same area as the Denon. You could either load you music files onto the laptop or have JRiver access them wirelessly from their current location. You can run JRiver on multiple PCs with the same license. You can set up JRemote to access either PC using the network access keys of JRiver. I only suggest extending you JRiver system because you already have it installed and working and because it works well for me on multiple systems.

Can you run speaker wires from you existing JRIver setup? It might be just as easy to add a small amp to that setup to drive the outdoor speakers?

Looks like I need to investigate which signal on the Denon can be mapped to zone 2. I was assuming that I could just use my old Vlink (I have two) and my wife's laptop to send digital signals into the Denon's DAC, then get that out to zone 2, but I'll have to look. Did not know you could run Jriver on multiple laptops, that helps.
I could run wire from my basement system out to the tub, but there isn't any way to control volume while using Jplay. Using the AVR, I could use an app on the iPad to control the Denon's volume, and select music with Jremote...but the run from the basement office would be a shorter run. My DAC has two sets of outputs, one balanced, so I'd have to buy those interconnects along with the second amp...and I'm running conduit and wire with the AVR route anyway, so I think I'll go there and use what I have.

You can also use an outdoor volume control. Not as sexy as doing it on you iPad, but easy to do.