Hi Swillie
I’m not sure about the addition of another UR 824 as far as what you get but I do know that many guys have been successful with it, ie it works!!! I would imagine you would get the channel strip on all 16 channels, not sure about the outputs though. I use a Focusrite Octopre which adds 8 channels, nice preamps, works perfectly use it for drums mainly.
Best Regards
Dave