It is very likely that you will be able to configure your Slingbox with the new X1 DVR box. You may not even need to reconfigure a new virtual remote, as the RNG remotes tend to work with the X1 boxes already. If you do need to reconfigure the remote though, just follow the process you find in this article:
When you search for your cable box's model number using the process in the article, simply type "X1" (without the quotes) into the search field, and it'll bring up a couple remotes that should work (likely ones that look more like the "new" remote you get).
I haven't come across a situation yet where we could not get a Slingbox to work with an X1 box. You should be good to go
Hope this helps! Let us know if you come across any issues.