How to get a clean line in signal out of Behringer V-Ampire LX210 speakers

Hi All,

Ive got a very nice guitar combo amp, the Behringer V-Ampire LX210.

Obviously meant for processing guitar signals, but the manual gives an example with drum computer or CD player connected to it.

I have not managed so far to get a clean, original, full frequency sound out of the speaker from a line-in source (Roland drum kit or mobile phone music).

The output keeps sounding guitar-amp-like.

My question now is: should I be able to get an original full range output on the speakers (if so, how?), or will the amp or Bugera speaker set inside not cover the whole 20 Hz-20 kHz normal music range?