i just got the Logitech® Premium Stereo Headset. When i plug them into my speakers they sound with extremely god bass. When i unplug the speakers form my computer and plug the headphones straight into the back of my pc the bass is horrible and most of the quaility of the bass is gone. I updated all of my sound drivers and motherboard(onboard sound might be problem) drivers but no help. My motherboard is http://www.soyousa.com/products/pro... Bust it up

It has nothing to do with your drivers. The speakers output is meant for low impedence devices - typically computer speakers are rated 4 ohms each. Headphones for computers are relatively high impedence devices, and meant to be plugged into ports for Headphones or Line Out which are meant for high impedence devices. Your high impedence headphones were not meant to be plugged into speaker ouput jacks, and they will not sound like they should if you do that. If you plug to any other port at all for your sound card, it would be Line Out, which with lesser onboard sound may be the same port as for Headphones.

so how can i increase the impendance on my onboard sound? Bust it up

You can't - you would have to use something between the speakers out port and the headphones that would convert the low impedence to high impedence - it's essentially a tiny transformer with a few extra pieces thrown in. e.g. Radio Shack used to make an adapter like that so that you could use headphones connected to speaker outputs on a stereo amplifier - three or 4 wires to a 1/4" female jack in a cylindrical enclosure - but I haven't seen those in many years. They were meant for stereos that had no headphone jack, and they may or may not give you a good result. The speaker output of most more recent sound cards and onboard sound is not amplified. The jack you plugged the headpones into in your speakers is likely high impedence and may be amplified and it's volume can be changed with the volume control on the speakers, or it may be un-amplified.