I don't see what you're going to add with an 8" sub, when your mains already go to 30Hz and the STF-1 is -3dB at 32Hz. You'll need to step up to a more significant sub, if you ask me. Note also that the RTi8s are likely closer to 4 Ohm nominal with the jumper in place, not the 8 Ohms listed, and that may put a little strain on the receiver, so be aware of that.