lol i might be new but heres my 2-cents anyway (well untill a more experienced member corrects me anyway!!)ill answer what i know..
1)yes you can connect it from your pre out to your subwoofers line level in jack.
2)you can change your subwoofers "cutt-off"(where it starts to drop in base power)this will be tunable from say 40hz-100hz but this is dependant on the sub. since the rsw-15 is a very good performer down deep 121@30hz! I would say you could set the dial fairly low ( say 60-70) and still get descent power.
4)there will be a phase switchable between 0-180 (to intergratewith main speakers), a volume dial (to intergrate volume with speakers) and a frequency dial as explained above. I also think the rsw-15 as high lvl inputs and outputs meaning you can plug your speaker wiring straight through the sub and then out again to your mains in order to filter the low frequencies to the sub and have your mains only playing above the set cut off limit frequency..there for making less strain for your speakers.
5) I have never had the pleasure of actually hearing the rsw-15 [:$] but i have read some reviews on it.. although audio reviews are mostly sadly full of BS... the opinions vary, many say it is a very musical sub ( which is obviosly what you are after) and some say that it is best suited to home theatre.. but again you will have to wait for someone who knows there stuff to answer that one!!!
well thats all. I hope I helped if even a little!