Sadly the TSR-8 doesn't do that - in my experience, TASCAMs tend to mirror inputs in groups of 8, so the MSR16 can do that, e.g. echoing 1-8 to 9-16 and the MSR-24 can also echo 1-8 to 17-24, but the TSR-8 doesn't have provision for this.
I made up a pair of 4-way splitters so input 1 would be...