I often have the same problem with my groups. You might try to challenge them laterally with puzzle-like elements rather than to challenge their stats directly. Send them up against interesting scenarios which aren't easily solved by brute force and high stats (exsurgent infestation with critical data or personnel that have to be found and saved, prohibiting their ability to open up with guns blazing... for example). Alternatively, send them against smarter opponents and use tactics that invalidate many of their advantages, unless they start playing smarter themselves. When dealing with min/maxed characters, the trick isn't to challenge them by sending beefy things. The trick is to send them against things that require the players to think more than roll. However, maybe the playgroup min/maxes because they want to just clean house and tear through threats. In which case, you might want to play to that. One of my groups is full of players that love just killing and fighting, and would rather not enter the horror elements of the setting. So I have them play as erasure squads, sent in after the nukes have dropped on a Firewall red zone to clean up the mess that remains. Sometimes you just have to cave, if that's the sort of game they want to play.