Eagles,
I found a test tone source to be of value to me. You can download test tones off the internet (I don't know where, but I'm sure people here do). I bought a CD with the tones already on it from AV123 (see
here). However, I ordered mine before my SVS ever arrived, so I had it waiting.
Just setting the levels using your receivers test tones would be a good start.
My general advice is this...do what sounds good to you. For me, sometimes setting the sub to be at the same level as the other speakers just isn't enough bass. So, if you find that you want to turn it up louder (or set it lower), don't think that you have to stick with it being level with everything else. I've fallen into that trap before, thinking that it must be better. In the end, it's all about what makes you happy. You bought the equipment, you might as well enjoy it!