Options for 2 or 3 band active audio tone control circuits with quite steep frequency response
There is a real problem when using higher-order filters as tone controls at audio frequencies.  The phase response and delay that those filters introduce become additive and subtractive at various frequencies as the controls are adjusted.  

Early graphic equalizers are good example of this problem.  The frequency response changes in odd fashions as you make what should be minor changes to the different filters.  This is both audible and easily measured.

On the other hand, both peaking and shelving high-pass and low-pass filters use at the very ends of the audio spectrum don't have as much problem with this.  These high-pass and low-pass filters are often 2nd order filters (12 dB / octave) but I have seen even higher-order filters in older analog audio mixing consoles.

I suspect that what you are calling "bass" and "treble" controls on the DJ mixer you are referring to are, in fact, shelving high-pass and low-pass filters.