Trouble with sound processing when using Headphone outpput from Laptop

[tsrusa2002]

Hi,
I bought a vocopro amplifier CDG-600RF which has following inout specifications for Aux/DVD/Cassette input- 150MV/50 Ohms.
When I try to connect headphone output from laptop and try to process sound using amplifier features like- digital key control, or treble- it plays the sound intermittenly beyond a certain volume level. Meaning that I can change keys only at a 1/4th the volume level. If I try to increase volume beyond that, it shuts off (or plays music intermittently). So it appears that it is not able to process sound when it is coming from laptop.
When I user DVD player/cassette player audio out, it works fine.
I am using RCA cables when connecting DVD player, and RCA (with stereo jack on other side) using Laptop.
On talking to Vocopro they said that all these players have fixed high impedence sound which allows amplifer to do further processing easily, whereas a laptop's headphone output is low impedence.
Not sure what that means but can anyone help how this problem can be resolved. I have all my music on my computer. Is there an external sound card that can help or something else. I don't even know whats the difference between the differences in output from laptop or dvd player nor understand what impedence means.

[Krispy Kritter]

Try decreasing the volume control on the laptop. You are possibly overdriving the input of the amp. Typically, you would use the audio/line out jack and not the headphone jack.