I did a test tonight and took the choke coils off the connections to my subs. YECCHHHH!!! I then turned my subs around and pointed them at the back wall, but the nasty muddy midrange howl reflected off the back wall. Things got a whole lot better when I placed pillows between the subs and the wall, but I could still hear too much mid playing through them.
The moral of the story is you WILL need at least one choke coil (10mH inductor) in line with that sub to tame those mid frequencies. You can order those through the aformentioned companies, or even possibly find one at Radio Shack if they still cary those.
As for the nichrome wire, I'll have to look through my catalogs some more. It must have been in one of the industrial type catalogs like Grainger... To know how long to cut the pieces of nichrome wire, you either use a voltmeter to measure out the right amount, or you stretch it out and calculate it based upon the resistance per inch (cold).
Now the A speakers don't have to be at 16 ohms, but if you don't add resistance to the bookshelf speakers, you won't hear the subwoofer. Woofers need more energy, and since it will be tied to the same amp as the bookshelf speakers, you can't turn its volume up without also turning them up.