Try running it on the 1-3 Dimm slots, set 8-12-8-28 tRFC 128, Tref 13600, TCKE 5 tWCL 7 2.0 Vdimm ... don't tighten the subs... MSI trains differently then ASUS... could be you have to do it in a few steps...
Some remarks:
-1.98 volts for 2600Mhz only is not an awesome kit mate
-CPU volts differ from brand to brand, in general MSI needs a bit more
-you are comparing an optimized mITX versus a full blown ATX board, so timings will differ for sure