Noise on playback with my own Laptop

[xxyzz]

I have found that some songs come out very loud while with others I have to turn the volume all the way up. Unless I am doing something wrong. Here is my setup:

Monarch Computers Hornet Pro Small Form Factor Computer @ 2.8 GHz

1 GB Ram
160 GB Hard Drive
Sound Blaster Audigy 2
ATI Radeon 9600
Dell 15 inch Flat Panel monitor
Plextor 52x CD-RW drive
Amplifier-Yamaha EMX 660

The amp gets more background hum than I would like. I am running a 1/8 mini plug cable from the SoundBlaster Audigy 2 sound card (green connection) into a ¼ to 1/8 mini adapter then plugging this into one of the ¼ instrument inputs. I am not happy with the volume but it is better in this input then trying the AUX or one of the HI-Z or Line in connections. Is it possible to get an adapter to go into the Lo-z connection and will it make any dirrerence? Would a line conditioner get rid of my background hum or do all amp’s put out some hum? Please post back here [email deleted to block spammers].

Last but not least if you are expecting the same sound quality as using the disc and your karaoke player, there is a very BIG difference.