Hello and welcome!
First of all I want to state that Mir_Computers got his Jingsha X99-8D3 working with my modded Huananzhi BD4 BIOS in this post. In particular he used the “M2” region, but I would actually recommend that you follow Example 4 from this post instead and insert the ME region you already have (9.1.40).
But why am I talking about X99-8D3 when you have X99-D8? Well, I did a quick check with intel FITC. As expected, the ME region is identical between these two Jingsha boards. So probability is very high that you can get this working. Above 4G decoding and Rebar are enabled by default already in my modded BIOS.