I have now been sending Certified LATE RENT NOTICES each month, including full balances due.Tenant will not communicate with me, and had turned down a very gratuitous Cash for Keys proposal when this all started. 

Please also keep in mind, the borrower would be under bankruptcy protection, so you must be careful in how you communicate with the borrower and/or their attorney, so as to not violate the automatic bankruptcy protection.Your post didn't indicate what jurisdiction the bankruptcy was filed in, you should probably talk to a creditor rights bankruptcy attorney in that jurisdiction.I practice in Indiana, so my answers below are based off Indiana law/practices. 

Very swift process, amazing communication, etc.

All they do is take 10%, own your listing and are only communication relayers.

Collect any written communications like the lease, email, or text.

I have 2 tenants who stopped responding to any communication from my side.

As a listing agent, there are multiple ways to communicate this to buyers of your property.  

I had a similar thing, but posted the eviction notice (it is not banned where I am) and between when she stopped paying rent and communicating and moved out, we did an inspection, but the last few weeks she did a lot of damage mostly filthy (disgusting would be more accurate).On the plus side, they are out and you can rent it to someone else-who knows maybe market rent has gone up.  

Problems between landlords and property managers are usually based on communication.

Certified mail should do the trick but at least one other medium of communication would be a good idea.Best of Luck!