Mario, I had a DC system similar to yours and after lots of thinking about it, decided the 3HP blower motor assembly was the only part I wanted to keep. I designed my own collection system using 120mm steel ducting, an Oneida steel SDD, and a pair of Wynn 35BA filters and catch pans. My shop is in the below-grade basement of my house (with no external windows or access), and I am determined to contain all dust there and not let it make its way through the rest of the house.
Here's the finished system, with room under the filters for my compressor. The dust drops into a 35-gallon plastic trash can that is internally reinforced to keep it from collapsing.
Here is a view of the system before I added the filter box. Although not shown in these images, I use a bungee cord across the top of the plywood that attaches to the trash can handles. This gives extra compression between the trash can rim and the rubber gasket attached to the bottom of the plywood.
Here is a closeup of the blower assembly showing how I attached it to the wall. I used rubber isolation mounts in compression mode to minimize the vibration since my shop is directly below the dining room. This layout works very well and my wife tells me she can't tell when the DC system is running.
This is a closeup of the interface between the blower outlet and the filter box. I used section of 180mm flexible ducting and formed it into a rectangle that is slightly larger than the blower outlet. I would have preferred a straight path to the filter box, but I had to make do with the limitations of the closet I built before I had the DC components.
This is a view from the inside of the filter box showing the ducting and the pitot tube that connects to the external differential meter I use to monitor the filter efficiency. It works well, and I noticed after a long cutting session that the meter reading was increasing. The plastic trash can collapsed slightly and broke the seal at the bottom of the SDD. This allowed lots of dust to enter the filter box and started to clog the filters. After an hour of cleaning the filters, I reinforced the interior of the trash can with braces, and it hasn't collapsed since.
This is another view from inside the filter box showing how I attached the Wynn filters.