There’s no difference in PowerPoint handling from way back to 1.0 series. If it works in 1.7.8 then it should also work in 1.7.9 as they work the same way.
If it isn’t, then something has changed one of those registry entries, as those are the only thing that have any impact on that.
Our general advice is to pre-convert PowerPoint items to videos as this is far more reliable in production use, and plays across all the Xibo Players available too.