Well the way I look at it, you are feeding the stereo from a sound card, and then distributing that to your Tannoy speaks, I may be wrong here, but you could run the rca's (red & white) from your sound card to your new SVS input, and then from the sub outputs to your receiver input. Therefore you will be utilizing the crossover on the sub to run the Low freq. to your sub and everything else above that to your receiver...
Correct me if Im wrong here, or you ahve any other equipment hooked up to your reciever, which will change the way you will hook these items up, otherwise, you could also use the high level outputs from your receiver (speaker wires) to the sub, and then from there to your speakers.
Good luck, and don't forget to get a spl meter to test output levels here, but seeing as you are just doing 2 channel, then you may be able to forgo this procedure of level matching and just adjust your bass level with your ears...
Please inform us here as to what equipment is hooked up to your receiver, or is this just a 2 channel only rig. Im assuming that you don't want to be running all your music in pro-logic, correct.
PS: I have that monster of a sub as well, GREAT CHOICE !!!