Dell Wyse Optiplex 3000 Thin Client & ThinOS Issue

Hi there, 

I need some help please! 

We are currently using 5070's but had to purchase some new Dell Optiplex 3000 Thin Clients and I'm wanting to set them up using FTP/WDM. 

The new clients are running ThinOS version 9.1.4097 but it only gives me an option to connect using WMS. There is no option for WDM (Wyse device manager) or FTP. Please note currently we do not have a WMS server, only WDM (5.7.2). There are plans for WMS but not for a while.   

Is there anyway to connect these new Optiplex 3000 Thin Clients to our existing (admitedly old) WDM/FTP server? We tried downgrading the ThinOS to 8.6 but we ran into issues as I don't believe it's designed for it. Any help would be really appreciated.

Thanks,
Alex