Silvia v Kongo would probably be a pretty crap match to be honest. Kongo is kickboxer with absolutely no ground game, offence or defence. Sylvia is a striker with little ground game game, offence or defence. Neither has much submission ability; however, Sylvia did at least try some submissions against Monson (which was laughable as he would never have submitted an eight-time Abu Dhabi Heavyweight champion... oh if you don't know Abu Dhabi is an annual pure submission fighting tournament).
Both fighters would stay outside, Kongo would throw repeated kicks to the rib cage (ala his match versus CroCop) and Sylvia would look to land the one big knockout punch like he does in most fights. The only excitement would be in the clinch as both fighters are strong and have pretty good clinch games (Kongo with his knees and Sylvia with his muscle-takedown technique).
I don't see Kongo winning as he won't be able to out-muscle Sylvia as he did CroCop, which he really only did after he broke CroCop's rib at the end of the first round. I would see the outcome as an unanimous decision for Sylvia.