JBL subwoofer, can i replace the amp and driver? effectively??

faster100

Ok i have a older JBL psw 1200 its a big subwoofer enclosure 21" tall and 13 1/2" wide and 17" deep with a 12" driver and 120 watt rms amp, i really like the sub and have had it for 6 years, seems i have to have the gain almost all the way up, it looks like new but maybe worn out on the amp, can i upgrade the amp and the driver? Ok i know i can do this, But will it sound good or do i have things to figure when dealing with a subwoofer as i know speakers are tuned to specific speakers and placement and all that. SO can this be done with good results? The enclosure is really built nice and heavy also not like some of the cheap JBL speakers currently being sold. Thanks