If you want to distribute binaries or code based on the (A)GPLv3, or use them to serve content over the wire, you have to distribute the source code of the entire software project under the (A)GPLv3. If part of that software is proprietary and licensed in such a way that you can't or won't distribute its code under the (A)GPLv3 or a compatible license, then you can't use any of the (A)GPLv3 code at all.

Now, there is some unclear legality around the distribution of plug-ins to a standalone software package. Are you allowed to distribute a GPLv3 plug-in to a proprietary program, like a GPLv3 plugin for Visual Studio? Maybe. Are you allowed to sell a proprietary plug-in for a GPLv3 software, like a paid plug-in to Emacs? Again, maybe.

However, the chances for both go down significantly if the "plug-in" is distributed by the same company as the software itself, and if the plugin is critical to major functionality of that software.