I dont know how the non thx radio is set up, but for the thx, there is an amp for the speakers and one for the subs. If the non-thx is the same, then just unplug the subs from the amp.
What are you trying to accomplish?
Getting a tune ON your car? Do you mean music tune or performance tune? If you meant performance, you need an sct device to tranfer the tune to the pcm, but you also need a tune to be written and loaded on to the device. Contact torrie from fastpartsnetwork to buy the device and get a tune from him.