You are one experiment ahead of me if you are using deep sky stacker which I downloaded but haven't gotten to yet.
You should be able to reproduce my fumbling with the equipment you listed.
https://www.pentaxforums.com/forums/58-pentax-beginners-corner-q/252668-basic...-peasants.html
From the looks of your photos you are doing something wrong with the software or giving it the wrong exposures to stack since even with one exposure I was able to get far more stars to show up. I don't think there is a patch of sky that is truly that empty.
I also have no idea what full spectrum conversions do or why one would need it for astrophotography.
With deep sky stacker the picture I took would be much better because you could get the flame nebula which is just barely visible as a faint red smudge around Orions left most belt star to show up. The Orion nebula (m42?) is very visible in my photo.
You should also consider building a simple barn door tracker since anything longer than the exposures I was taking had visibly elongated stars when zoomed way in.
Also you should be stacking raw images if it allows that, I forget, I really need to look into that software.
EDIT: And to answer jfords question you stack to increase exposure because everything is so faint so you have to build up an image. Its supposed to make all the faint stars and nebula and whatnot show up without using crazy high ISO or several minute exposures and allow much smaller apertures to clarify the incoming light.