4k box compatible with Xfinity new updates

I have been having issues since September.   Xfinity themselves seem confused.  Finally a new tech told me that Xfinity did upgrades in the area and my box wasn’t compatible with the “MOCA” updates Xfinity made.  However, he installed a non 4K box, not sure why he would do that!  I have already spent $300 with an AV guy to get surround sound, since the new box doesnt have Audio ports.  My AV guy told me i dont have a 4k box.  When i go into the store repeatedly, they never have one in stock!  So, i need to order one that is compatible with XFINITY new uogrades.  Thats what TECH told me but no one at  XFINITY knows what that means!  Im ready to cancel!    Can anyone help?????