Really nice of you to write all that down, thanks! That is a lot of cables and I might have to get back to you when I start plugging them in 
So, I need four cables plus a t-piece.
I am still not sure about the second preamp. I guess I might try a tube one but will have to see where my budget takes me. But first I will get the ISA pre.
I usually record 24 bit / 88.2 Khz with my mr816x. Does this affect the choice of preamp?
I noticed a Blue Robbie pre + Blue kiwi bundle deal from Thomann. That might be a good deal as I probably am going to need to get a high quality vocal + acoustic microphone too.