EDIT: you just posted as I was going to
Interesting. I thought that 'Laptop' and 'CEOL Piccolo' were both zones. What is 'Laptop' here then if not a zone?
the Piccolo I believe is your DLNA device, the Denon right?? The reason the laptop was showing up was because you have BOTH machines running as servers. This might be "practical", but it is not good practice ... there is no master library and the system gets confused for remote playback as you have run into ...
OK sort of thought this what was going on.
Now you need to choose which is going to be the "server" machine.
Lets say its your Mac PB. On the mini, go back to my client screen shot, and make sure the options are client options are checked. Then UNCHECK the "Use Media Network ..." Just to check go to Options=>Start up and make sure "Media server" is not being launched on.
Now, I think you have to close down JRiver, frankly I forget, won't hurt
Go to the Powerbook, nothing to do except note the access key from the option panel. Optional: check that the MPB can be woken up on your LAN and that in the Startup options at least Media Server is set. Keep this on
Reboot the Mini. There are a couple ways of doing this, but one is from the tree Playing From =>Add Library. Now enter password and Access Key (you only have to do this once). The Library from the Power Book should appear. So should its playback zones. Now you can control its playback. As you have connected via Authentication method (with access key). You can now tag the MPBs library which has become the master library from the mini. Remember there are a few things you must do server side ... moving/renaming files; importing; covert art management. So either you do this from the MPB directly, or you install on both machines a remote desktop software (like TeamViewer ... Ithink it works for MAC). The back up of the server JRiver library file is the important one.
You can of course invert this and use the Mini as the server and the MPB as the client. You might want to rename on the client machine the "server" library in case you ever want to reload the Local library.
Hope this gets you sorted