iMac running very slow following installation of audio plugins. 5-10 second Beachball and lag for nearly all processes consistently.

I would uninstall CleanMyMac 4 using the Developer's uninstall instructions. Cleaning programs can ruin normal computer operations.

Try going to System Preferences/Users & Groups and remove all your login items. Restart the computer and see if Pro Tools works any better.

Is there a missing or bad 16 GB DIMM in Bank 0 DIMM1 memory slot?

The PACESupport bits look pretty old.

And yes, when things go weird, remove the add-on cleaners, add-on on anti-virus and anti-malware and security tools, and try again.

You are welcome. Are the plugins compatible with Sierra?

Remove CleanMyMac. Too many other users have suffered from performance issues using this software.

Then go through the EtreCheck report and do some house cleaning. If you no longer use it, remove it. If you are not sure, make sure you know how to get it back, and then remove it to see if you miss it. cruft accumulated over the years can have its own impact on your system.

Finally, this is just some advice going forward. Get another 16GB DIMM and put it into the Bank0/DIMM1 slot. This would NOT solve your performance issues, but equal sized pairs in opposites memory banks allows the Mac to use Interleaved memory. Interleaving memory tends to improve overall performance by 10 to 15%. Again, this is NOT your problem, and a 10% performance improvement will NOT make your beachballs go away. It is just a way to squeeze the most out of your Mac.

Why Interleaved memory. Current RAM technology requires 2 memory cycles to access data. The first cycle drains the capacitive charge from the memory location to read its value (lets says this is the DIMM in Bank 0). The 2nd cycle is re-writing the value back into the now all empty memory location. During the re-write cycle, the DIMM cannot be used.

Interleaved memory means if the program is accessing memory in a sequential manor, then the next memory access can come from Bank 1, and since Bank 1 is not doing a re-write, it is ready to read immediately. So while Bank 0 is doing its re-write, Bank 1 can be read. And while Bank 1 is doing its re-write, Bank 0 is again ready to read. So sequential memory access can proceed at 1 memory cycle per memory access.

The reason you only get 10-15% is because A) not all memory access is sequential, and B) CPUs run way faster than RAM, and depends on 1st and 2nd level very fast caches and sometimes 3rd level caches to provide faster memory access closer to the CPU. And I do mean closer because in 1 nanosecond an electrical signal can only travel about 1 foot (30.48cm). And nothing in a computer travels in a straight line, so the further the DIMM are from the CPU the more delay in accessing DIMM memory, so a memory cache is positioned much closer to the CPU. Generally the 1st level (and some of the 2nd level caches) are located on the CPU chip itself.

Again, Interleaved memory does not have anything to do with your beachballs, so just consider this something to address in the future when you can afford to by another 16GB DIMM.