From reading your post and looking at your pictures,this is my best guess without being able to actually look at the house.
The problem started once the gutter system was installed and if you notice where the downspout from the upper level exits on the porch roof it is in the corner of the home that is leaking. weather usually travels west to east, so in this case if a severe storm is travelling to wards the front of your home with high winds, it is possible for the large amount of water that is being dispensed out of the downspout to be blown back against the house and pushed up under the siding. I have seen a few homes in the past with flashing installed incorrectly and having this very problem. it’s my feeling that if it was a drip edge problem as you described, you would notice leaks upstairs also.