Can’t change my package manager on new install of Ubuntu 16.04 LTS
I want to change my operating system back to Ubuntu after using Elementary OS for a time. I am currently using it on a USB drive to test it. I tried to install some programs that I have come to enjoy on Elementary like Nylas N1 for email and Clementine for music to make sure that I could transfer all of my data. The Gnome software centre did not have Clementine as a searchable package. I tried to get it manually from the site and then install it, which also did not work through either the software center or trying to use the dpkg command in terminal. I decided to try and get a different package manager. I tried using the command-line to install the old Ubuntu software center, and got an error
E:Package 'software-center' has no installation candidate 
as shown in image below. I got the same error when I tried to install the synaptic package manager. It gives me the error
E: Package 'synaptic' has no installation candidate 
as shown in image below I also tried to compile the source for both programs, but could not figure out how to get them running off the source code. I found the .deb for the synaptic package manager but I was not able to install that either. Is there any way to get a different package manager on Ubuntu 16.04 LTS?
Thank you. Note: I am not new to linux, but am not very familiar with the particulars of the command-line or the syntax that goes along with it.