I understand that you want to be able to connect those Mac to the Slingbox. Even though your Mac's are not meeting the minimum speed requirements, Watch at Slingbox.com should work fine since the Lion OS is supported. Have a look at these articles:
Thanks for using our Answers Forum. I have an article, Problems with "grayed out" onscreen remote, and/or "Country not Supported" error message.
Hope this helps.
Sling Moderation Team.