Just experimented in Roon with creating a grouped zone consisting of an iPhone and an iPad and applied a DSP (Procedural EQ --> Mix --> map L to both L+R and R to L+R for each device respectively)… despite how bad the iPhone and iPad speakers are for music listening (especially that they are not matched), the result definitely gave a much better stereo image. However, I believe there may be a timing issue between the two. It is difficult to tell because the two devices sound so different.
Anyone else want to try this out (if you have two Roon Ready / RAAT devices in close proximity) and give their impressions?