I have Aego M 2.1 speakers and Sennheiser HD 598 headphones.  Currently I'm using onboard sound.  I'm thinking about purchasing a Xonar Essence ST sound card.  Would this be over-kill?

I have just bought a pair of Sennheiser HD 598's. I have these connected to my Edirol UA-4FX Midi device (http://www.rolandus.com/products/pro...?ProductId=758). The sound is a little better than my onboard sound (Realtek HD), though only when I use the "Low Boost" and "High Boost" knobs to...