I don't have any experience with DIY, but you might consider a used c-j PV10 or PV11L. They show up here pretty often. (My PV11 will probably show up here next year, but you probably don't want to wait that long!)
Either of these would give you a significant boost vs. the Denon. I've had mine since 1991 and it never fails to satisfy.
Either of these would give you a significant boost vs. the Denon. I've had mine since 1991 and it never fails to satisfy.