Reply to Soundcard Help!

Right, the thing is that i am a bedroom DJ.
I am a total noobie to all of these different types of inputs and outputs, so if anything it is advice that i need most.

I have a home HI-FI system which is the source of sound.. However i do not know which soundcard i should be looking for at all!
My Computer has 2 usb ports, no firewire but a USB to FIREWIRE adapter is a possibility if such a thing is neccesary.
at the moment i am using Traktor's internal mixer as i do not own a mixer myself.
Need cueing finction and prefferably a Good quality soundcard..
Can somebody please explain roughly what i need with maybe some soundcard suggestions..?

Thankyou all.

Joe.