I tend to agree with several posters recommending a better integrated (Orpheus, Soix). To me it seems that you have 2 componentes holding you back (the preamp in the receiver and the amp in the receiver) and you are considering which one to upgrade. Unless you plan to upgrade 1 now and 1 later I think it would be best to upgrade them both now. A good integrated anywhere near the $2K mark (especially used) would seem to me to be better than either a great preamp + the Yamaha amp or the Yamaha pre section + a great amp.
Just my 2 cents especially considering I'm not familiar with your Yamaha or other gear
Just my 2 cents especially considering I'm not familiar with your Yamaha or other gear