Right, you can't use the 'tape out' connections because they're not controlled by the volume control on the preamp, meaning the volume coming from the sub wouldn't change as you adjust the volume to your main speakers.
If you do want to split the preamp output you can use one of the devices Steuspeed recommended. He suggested one from Audioquest and there's another from Monster. Click here to see what the one from Monster looks like. Both it and the Audioquest version are solid connectors, no wire involved.
You shouldn't worry about using the speaker wire connection method, though. The subwoofer amp won't be pulling any substantial power from your main amp and won't overload it at all. That connection method is the one recommended by both REL and HSU, makers of some of the better subs out there. You should definitely do what you're most comfortable with, however, it's your gear.
If you do want to split the preamp output you can use one of the devices Steuspeed recommended. He suggested one from Audioquest and there's another from Monster. Click here to see what the one from Monster looks like. Both it and the Audioquest version are solid connectors, no wire involved.
You shouldn't worry about using the speaker wire connection method, though. The subwoofer amp won't be pulling any substantial power from your main amp and won't overload it at all. That connection method is the one recommended by both REL and HSU, makers of some of the better subs out there. You should definitely do what you're most comfortable with, however, it's your gear.