Ignore the app. Make sure the amp’s positive (red) terminal is connected to the speaker’s positive terminal and the amp’s negative (black) terminal to the speaker’s negative terminal. On both speakers. If one speaker was connected backwards, the bass is out of phase and will cancel out.
If the speakers are connected correctly (see above) and they are still too bright, try replacing the positive terminal strap that connects the upper and lower positive speaker terminals with a small value resistor and connect your speaker cables to the lower set of terminals. 1 ohm, 1.5 ohm or 2 ohms will drop the level of the midrange and and high frequencies a touch, more with the higher values. 5 or 10 watt resistors are far cheaper than new speakers! And before I get roasted for modifying the crossover, please note that Wilson, Magnepan and others offer this same option to tune the level of their high frequencies, too. Those M-L speakers are excellent, don’t give up on them!