You can replace with 2 widow bucket seats, and install subwoofer, but it will not be a good idea as people sitting near woofer will feel uneasy. Secondly this will create less place then what already is.
Either way i dont see it to be a win win situation as your hilux SR5 is multi utility...
My Dear, Jason. The choice always can be made based on how many bucks you have at disposal? Starting from 850$ you can configure good musci system.
A lot of info is needed before we start
Whats the car type? What speakers it takes? Wether it takes dual dinn ot single dinn headunit? Ho many...