optimus sts 1500 speaker diagnose help

Hello, I was hoping someone could help me figure out what is wrong with my purchased new in '91 sts 1500's . These speakers are like new and have been well taken care of but I hooked up some old Kenwood speakers to my pristine Sansui 990db and they sounded way better than my Optimus'so now I am realizing these 1500's have been bad for awhile and I have just been turning up the amp and not noticing they dont work right.I know some people would say get rid of them but I like big things and these are big , they both sound muffled and are not putting out. Where do I start? I Know, get some jbl4430's and that sansui will blow up your f*****g house but I want to fix these first. Any help is greatly appreciated.