If you're looking for a denon receiver, there is a 4306 for sale for $650 on videogon. Beautiful unit, and has hdmi as well. Retailed for around $2000.
http://cgi.videogon.com/cgi-bin/cl.pl?rcvr71ch&1240348794
With a $6000 budget, I would look into getting a separate pre amp/processor and...