factory amp

Would the factory jbl amp downgade my sound system since I'm using a new head unit , speakers and amp for new sub. The way it is set up now the speakers run from the new head unit back to the jbl ampin the trunk and then back to the speakers. I know that in 89 this probaly sounded good but the new stuff I have should sound better if I by pass the old amp? Right or Wrong?
Thanks,
Joe

I can only speak for myself, but I replaced the JBL with a decent kenwood 75Wx4 unit and it sound tremendously better.