Many amps dont have adjustments for treble and bass.
The sound comes from your dvd player via the digital cable and out through the speakers as it should be - in its original form so there is no need to adjust bass /treble etc.
However if your personal preference is to mess about with the sound then any decent amp will have a selection of preset modes for various types of programming .
Eg: games ,music , movie,mono,sci-fi and many more where the sound will be changed .
That should do the job for you