And in fact, that's an excellent way to get your feet wet in separates. By upgrading your amplifier to a separate one of high quality (such as the 770), you'll make a solid improvement to your system without having to buy a whole ton of components initially.
Later, you could, say, get a separate tuner. Then you'd only be using the pre-amp and surround processing of your receiever.
Finally, you could buy a surround processor and sell the receiver.
Jeff