Unless something the AVR230 is broken, stick with it. The other two receivers mentioned might have more features but I'm betting the sound will about the same or worse overall. I'm still using a high end 2001 receiver and loving every minute of it. Don't miss all those new features at all. If you want to get a new receiver, save your money for a real upgrade that will be a big improvement on the AVR230. I'm talking about spending more than $900 on a high end receiver that will be much better in quality, durability, power and features.
They are of little use if the receiver does a poor job of delivering the sound to the speakers.
The TV should do a good job of that.
