Thank you @Barry and @Gaurav for your valuable suggestions.
After reading Gauravs topic, decided to go with speaker replacement instead of sub-woofer.
Since I do not have any idea on this topic and if I go to any dealer they can make me fool easily and install any kind of speakers, so I need some more suggestions--
1) Which speakers (for back and front) are good which produce good bass and clear sound in my Nissan X-trail.
2) budgeted speakers, my budget is around AED 1K. Not sure if it's very minimal but this is what my budget is.
3) since my car is brand new (month old) does changing speakers void my warranty? if I do it outside?
4) Any good dealer who can sell/install speakers??
Thank you