We are getting ready to move existing content into Guru. We have previously used a combination of Sharepoint and a Wiki. In Sharepoint most of the content is office files, Excel, Word and Powerpoint. Much of this content is not appropriate to change to card content. Like Excel files with multiple sheets containing many rows or Word files that use our company branded template. 
The disadvantage of adding the files as attachments in Guru is that it is a quite cumbersome process to download the file, make changes, upload a new file, and remove the old attachment. 
The iFrame option is also not a good option for us because we have different user authentication providers for Guru and Sharepoint. 
The third option we have as far as I can see is to create url links in Guru to Sharepoint location of the files, but one of our goals is to reduce the number of systems used for storing knowledge content. We would then be forced to keep Sharepoint. 
I guess this is a quite common problem case with Office file content. I will appreciate if any of you have any tips or best practices to recommend.