This is also true, LFE+Mains is a setting that is for the Large setting only.
This should be set to LFE , speakers to Small and then experiment with the crossover point. The crossover point that should work the best will be determined by how low your speakers go and what makes a good blending point for your subwoofer and speaker.
Again using Large means NO crossover is used, even if you can set a crossover point it does nothing.
Also yes it's very true to use what sounds the best, however with a little learning and experimenting you can discover what really does sound the best. There is a lot of difference between a hodge podge this sounds good and a well calibrated system, if you really want your systems sound quality to shine it takes a little learning and some experimentation.
You mean when set to Small I can set my Fortes to Xover at 40hz?