Your right the real issue is that VNC does not support audio.
Connect To Mac With Vnc
Screens is a powerful VNC client app that lets you control any computer from anywhere as if you were sitting in front of it! . A VNC Server, such as UltraVNC or TightVNC, is required to connect to a Windows PC. Windows, Linux PCs and Raspberry Pi can only send or receive text and URLs. Screens will not receive any sound from your computer. This is a limitation of the RFB protocol the app is using. Screens Connect requires OS X 10.6.8 Snow Leopard or later.
The TightVNC Server and Viewer use special data encoding techniques designed to. Apple Remote Desktop is used to remotely manage Mac computers in a commercial or business environment. Screen sharing and Apple Remote Desktop screen sharing are compatible with Virtual Network Computing (VNC), an industry standard for controlling.
Logic pro for apple mac. Apple's Screen Sharing, ARD aka Remote Desktop and Back-to-my-Mac all are based on VNC code so all also lack the ability to include remote audio support.
Actually, there isn't a Nitro for Mac version. Nitro only works on Windows. If you've ever tried to find out whether Nitro can runs on Mac, you would be told on Nitro's official blog that you need virtualization software like VMware Fusion or Parallels Desktop for Mac to run Windows first and then install Nitro in Windows that is virtualized. 
Nitro Pro by Nitro Software, Inc. Is a very popular PDF management tool that allows you to create, edit, sign, convert and even share your PDF documents with other users. Sadly, Nitro Pro for Mac has not been released just yet, but there are lots of alternative applications that can help you work wit PDF documents. Nitro pdf reader free download - Adobe Acrobat Reader DC, PDF Reader Plus, PDF Reader Pro, and many more programs. (Mac) Free to try Infix PDF Editor (Mac) Edit PDF documents just like using a.
The most common solution that does include at least some audio support is Microsoft's Remote Desktop Protocol as used in their Terminal Server and RDP client. I would not be surprised if their Mac client like most of their Mac software is crippled in this area.
Hypothetically you could run a RDP compatible server on one Mac and a RDP client on the other Mac. With regards to an RDP compatible server for the Mac - Microsoft do not do one but have a look at these.
http://www.aquaconnect.net/ignision-server (expensive and audio not yet added)
http://www.coderebel.com/products/irapp/ (a bit cheaper claims to already support audio)
https://github.com/FreeRDP/FreeRDP/wiki/PreBuilds (free but requires more work to install, not sure if it supports audio but RDP as a protocol does)
Screens Vnc For Mac Osx
See this comparison table https://en.wikipedia.org/wiki/Comparison_of_remote_desktop_software
Mac Os X Vnc Client
Vnc For Mac
Vnc Viewer For Mac Os
I would not normally recommend making RDP access possible directly over the Internet. I would instead recommend you first establish a VPN connection to your LAN and then access RDP via the VPN connection. This is to prevent hackers breaking in and controlling your computers.