Help Choosing Audio Card/headset

[FocalFury]

Hello all.
I am getting ready to build a new rig and have all the components picked out.
What I'm not as sure and ready about is my audio card/headset I want to use.

I have a Logitech X-540 speaker set (5.1)
I will be getting the Asus P6T6 Motherboard
I am a gamer and do listen to music etc.

First off....is the improvement substantial enough to need a standalone sound card from onboard audio?

My thoughts are if I do get a card would be an X-Fi Titanium Fatality.

Heres the next part where I go back and forth.
I'll be playing some MMO games where I'll be using Ventrilo always.

My initial thought is that I'd like only a headset that goes over 1 ear to hear all of my friends talking to me and have the game coming through the 5.1 system.
I choose this as I'd prefer...because I will be using ventrilo so often...to not get enveloped in a 5.1 headset for HOURS ON HOURS all day and take them off and feel like im getting out of a fog.

Or maybe I'm crazy

a final note is that I live alone and so loud speakers rather than a headset is no concern.

I'd appreciate hearing peoples opinions on what they would do and what equipment you would choose

Thanks

D A N N Y