Hello !
I'm happy to read your post because I use the DNS320 too, and I thought that I was the last person on 2020 haha.
First of all I advise you to upgrade the firmware to the last version to avoid Cr1pT0r ransomware.
See http://forums.dlink.comindex.php?topic=74741.0 to download the last firmware.
I've recently discover that we can use the plungins from the website down bellow on this NAS (Even if the compatibility says no) :
http://dlink.vtverdohleb.org.ua/Add-On/
We just need to convert the plugin to DNS320 format with a module of the SDK of D-link (mkapkg) on linux.
Thanks to ACME_Corp (http://forums.dlink.com/index.php?topic=62804.0)
Using the SDK I've managed to convert DNS-320L addons to DNS-320B.
HOWTO:
Download the package you want to convert (DNS-320L Twonky Package v2.06_07212015_UA)
Extract the files with binwalk :
binwalk -v -e "Twonky Package v2.06_07212015_UA"
Untar the generated C8 file "tar -xvf C8"
Enter the newly created directory "cd Twonky"
Generate the package for DNS - 320B "mkapkg -m DNS-320B"
Now you can upload the package to your NAS using "/web/app_mgr/module.html" wich is inside it but somehow disabled.
Navigate to Administration / Application Management / Right click on Multimedia Services / Inspect Element
and change /web/app_mgr/media_share.html to /web/app_mgr/module.html now click on Multimedia Services and then you just got to select the file previously created "DNS-320B Twonky Package v2.06_07212015(BETA)" and Apply. Once it's been uploaded and installed you can enable it.
With that you can install transmission, openvpn, telnet, ssh, PLEX ?, and many more.
You can try an alternative firmware "ALT-F" https://sourceforge.net/projects/alt-f/
To process it's very simple, you need to download the firmware update on Sourceforge, and go to the admin webpage, in the upgrade page, upload the firmware.
Alt-f will be install after the reboot (Dont panic your file will be conserved, the upgrade don't erase the disk).
If you want to return to the original Dlink firmware do the same process in reverse, upload the DLINK Firmware in the upgrade section of ALT-F.
With this firmware you have the possibility to have more recent version of SMB, FTP etc ...
I don't know if all this information will help you,
I hope,
Stay safe,
Pierre,