Hi all -- I'm looking to purchase a new receiver for home theater and my max budget is $300. I've read through lots of threads here and have decided to go with Panasonic. Sounds like they offer the most bang for the buck. I am confused by the different model numbers. What is the difference between the SA-HE200, SA-XR45, SA-XR50, SA-XR70? And the panassonic website is of no help at all. thanks in advance for your help!