If you go with that sound interface I showed you then that will be for INPUTING sound, I'm pretty sure you can monitor with it to. You won't need another sound card though to go with it as there is one in the motherboard you can use for your speakers,
Anyway here's my advice to you, and I'll start by the bits you can keep from your current system -
Case, hard drive and DVD drive.
Then purchase -
An Intel i5-4430 CPU
A Gigabyte GA-H87M-HD3 mo/no
Ram go with 4gb (for now)
CorsairVengeance Low Profi 4GB DDR3 1600 MHz
Power supply Corsair CP-9020047-UK 500w
This came to around £250 on scan.co.uk, apologies if your American lol
You will see one hell of a power jump with this set up and is upgrade able for the future. It's quad core, has the 4th generation (just out) core CPU. And the latest intel hd graphics, which although a lot a people slate, you'd be pleasantly surprised with the gAmes they can run.
Lastly you mentioned an SSD ? I think you meant. you would see an increase in load times, but IMO It's an unnecessary budget hike for now, when you need money for recording equipment.