does anyone know if the arc ks 125.4 mini will fit under the seats without cutting the air ducts?

What are the dimensions on it?

10.25(L)x4.8(W)x1.7(H)

Nope, cutting will be needed. I put this under my seat, similar dimensions and it definitely needed cutting. Just the duct itself though, no other cutting required. It's easy and you'll never know the difference.

http://www.crutchfield.com/App/Product/Item/Main.aspx?g=120&i=023THA475P&tp=115

thanks for the info

ill keep you guys updated on the install

anyone know if you have to cut for the Infinity Reference 5350a?

The best way to figure out if you can fit the amp (if you don't have it already), is to make a mock up with cardboard. Just cut it out and tape it together to the dimensions of the amp. Then go see if it fits.