Both are good system..
Denon x500 advantage : Powerful than YHT2910..U can able to extend your upto 165 watts per channel in future.As a user I'm enjoying this system a lot.
YHT 2910 advantage: Have more features than x 500 such as 4k passthrough,USB plugin option for audio,ecomode option .This year model of Yamaha.
As per many members review denon x500 is good with Boston Acoustis soundware XS 5.1 speaker system.
You need decide it based on your budget and ur hearing taste by proper audition.