i have a 10 w6v2 in a 4080 box and I wanted more volume. I listen to my music really loud all the time so i also wanted to do it so i can get the volume i have now without stressing the speaker so much.

will getting a seccond 10w6 make a big diffrence?

 

Adding a second sub will make a difference if you get a more powerful amp. Using the same amp and splitting the power isn't going to do much for you.

 

theoretically adding a sub will double your surface area and your loudness (+3 db)

but will put a bigger load on your amp

1 sub = X ohms
2 subs = X/2 ohms or 2X ohms
aka 2 subs draw twice as much power or half as much power (i don't imagine you would choose this option)

(X is a variable)

now theoretically twice power is another +3 db. so yes i would say another sub will make a big difference. now you are stuck do you want to stress a sub or an amp