So do you want a sub just to add onto the bottom end? Or would you like to improve on some of the midbass that the Airmotiv is producing? I thought the midbass on the Airmotivs was a touch muddy, compared to what I'm used to (not bad for a little 4", though).
The SB-1000 is not really bigger than the M8. It's an ultra compact 12" sealed sub, a 13" cube. But you will feel either sub some if you turn it up and your room is not too large, with the SB-1000 with the potential to get louder without losing composure. And the SB-1000 is just a better SQ sub.
As for blu-rays, a sub would make a difference.
As for pre-amps, I use an Schiit Asgard 2 headphone amp that has pre-amp outs. Awesome headphone amp, and works great as a pre-amp, too
Edited by cel4145 - 4/8/14 at 8:46pm