Have you considered changing out your Marantz pre-pro with a different one? If you get a processor with even a slightly higher channel count, you can have your front wides as well as all the other speakers active. Just make sure that the unit can be upgraded to DTS: X Pro whenever that is added to units outside of the Trinnov. I don't recommend Emotiva processors given their track record, however.
The Marantz has 15.2 channels available, but it can only process and output 13.2 at a time. Also, it won't use the Wide channels on anything except native Atmos content that has metadata for Wides. The DSU won't use them under any circumstance, and DTS NeuralX will only use them if the Rear Surrounds are disabled.
Do you know of a processor that can output 13 to 15 channels simultaneously, or will use the Wides for both upmixers, without going to the expense of something like a Trinnov or DataSat? I am not aware of any, nor am I aware of any (more) affordable processors that are coming out with DTS:X Pro capability. If you know of something... I'm all ears!
In the Triad thread, you asked about my backboxes for the RSL C32e's. They are built out of 3/4" MDF. They 23.75" square and 5.5 " tall, Outside Dimensions. This makes the internal volume 1,980 cubic inches. One cubic foot is 1728 cubic inches, so my boxes are 1.15 cubic feet, which is close enough to the RSL recommended 1.2 cubic feet. The internal seams are sealed with rubber caulking and the boxes are stuffed with polyfill. They are 1/4" shy of 2' x 2' and that allows them to drop perfectly and snugly into my 2 x 2 ceiling gridwork.