Unable to Connect to iTunes Library from Apple TV

Hi guys!

I am using my iMac as a router (I enabled Internet Sharing via WiFi) so other iOS devices can be connect to its WiFi network.

Since OS X El Capitan upgrade I cannot share my iTunes library from Apple TV (3rd generation). I tried to use my Personal Hotspot via iPad and my Apple TV can share it properly ( I can share iTunes library on iPad and iPhone without any problems).

I contacted my wireless carrier who opened all ports which Apple products use but the issue persists. So he suggested me to let iMac see "input port" or IP address of Apple TV but I wonder if it is possible. I have already restored Apple TV as new, disabled firewall, renamed iTunes library and computer's name, logged out form iTunes and relogged into it, disabled Home Sharing and re-enabled.

Could it be a software update issue? Or should I purchase a WiFi router?

Thank you so much to all.