I really do not know how the parameters affect the bass enhancement as it sort of implies that there could perhaps be a separate low frequency channel too somewhere. Maybe this is possible as I know an LFE/sub output is part of the configuration somewhere, but who knows.
I'm assuming that harmonic content would determine how many additional harmonics are generated. Some % might = 2nd harmonic only, a higher % might mean 2nd and 3rd are generated etc.
Effect strength vs mixing balance is confusing as I could see both of them doing exactly the same thing. In other words how much of these additional harmonics are added to the original sound.
The high-pass corner implies the -3dB point for a high pass that would ordinarily protect the speaker from frequencies it cannot produce. Obviously we've no idea what the slope type used is.
The low-pass corner could be asking how high up in frequency do you want the additional harmonics to be added, or it could be how high up do you want the enhancement to detect the presence of the bass fundamental.
The crossover frequency is kind of bizarre as a parameter for this.
Without an explanation as to what the settings do you're just going to have to give it a go and see.
If you wanted to quantify the results you could connect the output of the bluetooth module to the input of a soundcard. Play sine tones and white noise as stimuli on a phone with an appropriate app and then alter the parameters of the enhancement and see what happens.
Thanks a lot for that clarification.
I would like to add my experience about three options:
Effect strength - this is a percent of increasing bass
Mixing balance - this setting defined proportion between bass and hight\midle sound.
The crossover frequency - defines what exactly is a bass and what is a hight\midle. This is need for Mixing balance percent. In other words, if you set crossover frequency 150Hz and Mixing Balance 40%, the frequencies before 150Hz will play only on 40 percent, and frequencies after 150Hz will play on 60%.
Just in case, I'm not an expert on this, this is only my experience of configuring bass enhancing.