I asked Rick at Audio Images (I bought my DSW and other items from him) about my issue and he agreed that the 4k version probably has greater bandwidth than the standard Bluray although that doesn't account for your condition.

Paraphrasing his reply he gave me solutions.

"" Either:
Keep the overall volume to a level where it handles the signal,
Or
Limit the DSW signal as I suggested in the Meridian Surround Controller config
Or
Get a Sub which will handle the signal at the volume you require ""

I go for the first solution as the instances are quite short and so far only apply to a couple of my films.

I'm not experienced enough to answer your other queries about a second DSW. Also any extra purchase is beyond my means at the moment sadly!

Regards
Bob

861v8, UHD722v2, 5200s, 5200HCSEup, M6s, 3200s, DSW, Sony 55A95L, Oppo 203, Sky Q Silver
Samsung QE43Q65B, Oppo 105 & Sky Q Mini