Many babies have this meltdown at the end of the day and I think it is often caused by over tiredness and over stimulation. Does he nap much during the day?
In addition to making sure he is getting enough sleep during the day another thing that helps if it is over tiredness and overstimulation is to be very low key and quiet with him for the hour or two that usually proceeds the meltdown. I see you have five older children (God bless you!). I wonder if all the activity is just too much for him? Some babies just have a lower threshold for stimulation and get overwhelmed more easily than others. My middle child was like that.