Looking to upgrade from receiver

Hi, I am looking to upgrade from an 11 yr old Onkyo 100W receiver. I currently have B&W DM604 speakers and would like to upgrade to seperates or an integrated amp. Looking to buy used with a budget of around $600. I mostly listen to Jazz and Classical. Listening room is rather small. It seems to me that an integrated would give me a bit more quality for my budget. All comments are appreciated.

Thanks,