If it's not up to the job ditch it and use the cash to fund your new system. Either way you will be upgrading speakers so start there first. When it comes to the speakers spend your money on the fronts there the ones you will here, rears on a standard system are really only sound fillers or for back seat passengers. I am still using the cheapo paper oem rears on my car and even though I am the wrong side of 40 I have a sub in the boot which transforms the listening experience as every speaker is doing its proper job and not under pressure and to be honest volume levels are in fact lower,think of it as a small engined car screaming down the road at a 100mph as apposed to a big v8 doing the same 100mph effortless.