Your Sony probably sounds great. Your new receiver will sound better, but that's only because your mind will be telling you so. Maybe at very high listening levels they could actually sound better, but if I were you I would keep your current receiver and use the money on something that will definetly improve the sound- like an EP500.

If you are definite about getting a new receiver, buy the one that you think looks the coolest because you can't go wrong either way.