Well this is a surprise. But yeah no active noise canceling headphones can touch the Bose qc15. if you EQ them they can sound pretty good as well. They don't play the loudest but are very comfortable.
Perhaps it was just the set i was listening to but the sp2500's sub wasn't very good. The woofer seemed to bottom out before it could get very low. But as i said that could have been the particular set i was listening to.
That little onkyo shoud be good and paired with a subwoofer amp to power...
Why not buy a 2.1 amp and wire all your speakers as passives to it? I have seen a few amps that are 2.1 Parts express and madisound have 2.1 plate amps and there are many 2.1 t amps. You will need a pair of crossovers as well due to the speakers being bi amped.
If there is enough wire left over you can just splice it via Soldering or butt connectors. If its not the control box wires it will only be 2 wires. Wait did you have your dog put down over it chewing your $100 dollar computer speakers? I guess its none of my business but.... Jeez.
Back with some of my older computers I had access to tons of 120mm by 38mm server fans that where loud loud loud and it was common practice to cut the molex connecters so i could run 5 volt. As for 7 volts i cant say.
On a side note its good to see you upgraded your computer.
If i wanted a neutral headphone i would look at the Brainwavz HM5 headphones. The DT headphones sound very good but they are not the most neutral headphones.
http://www.amazon.com/Brainwavz-HM5-Studio-Monitor-Headphones/dp/B006MA9XXM