Infinity Kappa Perfect 10.1

Those are top notch SQ subs.  I was surprised to see Crutchfield has them for $70 off ($179.99 with a free box).  I remember back when these subs first came out they were $299.99, and even at the time I considered them worth every penny.  Looks like right now you can get them at a very attractive price.

I haven't heard the new Kappa Perfect VQ subs yet, but supposedly you can adjust them to match whatever your enclosure size is.  Too bad you'll pay at least $100 more for them.

Anyways, when you put the 10.1's in the proper enclosure they hit really deep and accurate, without any booming.  For SQ I'd go with a small sealed box, 0.6 cu. ft. as recommended by infinity.

The DVC models are worth looking at if your amp requires a single 4-ohm load to maximize its power output.  However, if you have an amp that can handle a 2-ohm mono load then the SVCs are a better deal.

Yeah I'll throw in.  I hear a Kappa Perfect 12.1 and was VERY impressed with it.  Just one sounded better than most pairs of subs that I've heard.  Infinity did a great job on that line.