You're playing the #8 seed from the other coference. Surely you can win that game without playing your starters and on TIE. He only has one good player and his gameshape is crap. The other game you can play your starters and TIE and probably win as well, so then you can go normal or CT with the cup game.
The other advantage of going an extra round in the cup is that it means you get three training games next week so you can train whatever you like rather than being "forced" to train stamina or FT because you only have two games with trainable minutes. It also means it gives you an extra game to recover your enthusiasm, so if you end up facing another top team you can just TIE for that game when everyone else in your league will be having their enthusiasm decaying back to 5.