If you tell us what you need to know or what you are looking in this system we will give feedback. There are plenty of reviews of 506 in the net. Let us know your specific requirement so we can confuse you more (just kidding)
Its a decent AVR. What speakers are you pairing it with and what you hope to listen to for music?
Let us know your budget for speakers so that we can give you some options.
15K is too less for 5.1 . But since you have front speakers already, would suggest you to go for Yamaha power cube subwoofer. I have seen it in Croma and price varies between 6 to 8K. You can go for wharfedale centre speaker WH2-C, and it costs 5 K. Still you have remaining 3 - 4 k which you can use for rears.
This way you can start with 5.1, and slowly replace sony fronts with wharfedale 9.1 or 9.5 depending on the budget.
One more way is that i have seen onkyo and yamaha selling fronts + centre as a package for for 7k or 8k. If you buy those then you will get timbre matching too.
Thank your Spirovious,
Can you give any model no. so that I can search the web
Gap G J