Nice Amp

I got the same Sony as you and dont really think much of its sound quality, I also have a Kenwood which has good sound quality but wont read disks now, and I currently have an old Alpine Cassete/Changer in my Sierra which is ok but not up to much now.
I would personally go for another Alpine unit to replace it as I think they have really good sound quality and arent full of useless shit that you dont need, they serve a purpose and they do it well.