Infinity White Background Problems

I have 2 Westcott TD6 Spiderlites with shallow 36x48 soft boxes and 2 Calumet Quattro lights.

I have the quattro lights at a 45 degree angle to the white paper background and the spiderlites at a 45 degree angle to the subject (the subject is about 6 feet from the background).

The result is attached (

). It's basically a grayish-white, nothing compared to these super white photos I see. It's crazy because there is just so much light when the subject is in there.

How do people get it SUPER white? Is that editing or can that actually be produced? What am I doing wrong?

Thanks!