How to save preferences for use across multiple desktops?

Preferences of Acrobat DC are automatically shared across computers when you are logged in (except for Add-On tools).

I don't know for Acrobat XI.

The answer to this question is a may be yes and may be no.

It depends on many factors.

See this guidance on how to reset preferences:

https://helpx.adobe.com/acrobat/using/workspace-basics.html 

Now, the link above only covers on a single computer.

So, it is possible to backup and restore a directory with user preferences to be used with a new account.

But if you're in a network environment, that is accomplished via user roaming profiles and administrative Group Policy templates that are enforced and centralized from a server.

Also, keep in mind licensing criteria considerations.

You can't just copy user preferences  from a windows 10 machine with Acrobat Pro DC with a monthly paid subscription and  go and paste it somewhere in another machine that runs with an older  of Windows and/or a different licensing track od Adobe Acrobat Pro, for example.

For this to work the best you need to have every computer with the same hardware specs, the same operating system version and updates applied, the same Adobe Acrobat product and same version updates applied, and  keep in mind that even so, if you have a paid subscription, you cannot use your current subscription with the same AdobeID in more than one computer simultaneously. You'll always must sign out first from one computer device before you sign in in another.

If this is a network setting environment ask your IT Manager if they can create for you a user roaming profle.

It is the IT department responsibility to administer user accounts, and the handling of the licensing and updates  requirements when you need this type of setup.