Well for fuck sake then!
Seriously, the 824 gives you quite a bit of options. Well, with Cubase anyway. Not sure how reaper deals with the outs and monitor mixes.
Having 8 outs from the interface gives you much flexibility. I have two of the 824's just to keep consistent. The second is running as an ADAT slave. I can also use those inputs/outs for whatever needed. I also run a Behri Ultragain for the other 8 ADAT tracks in case I need more tracks when recording. Hasn't happened yet but I figured $100 to make sure.
Within Reaper you should be able to create separate mixes to the outputs of the 824. You would need separate headphone amps or one with AUX inputs to make this happen, but the benefits of not adding the noise from a lesser preamp at the input stage will be a benefit in the end result for sure.
The pad on the 824 makes the use of external preamps through the interfaces preamp a non issue. I use a Vintech X73i as my 'sweet' channel into the 824. No noise issues with the combined preamps at all. In fact, I really have to push the Neve clone to get any noticeable noise.
I would love to see your setup sometime. Seems we have quite a bit in common.