I think your speakers are 90dB sensitivity so not that hard for any amp to drive. Obviously more headroom is always going to be welcome but it's the processing power of the AV amp that is just, or perhaps more, important that outright power. That can always be augmented at a later date if you feel the need to do so.Do you think my speakers are too old and maybe i should upgrade the speakers instead of the receiver?
The more speakers you add to any AV amp then that power has to be taken from a single PSU and it's likely that with a full speaker load in very active scenes the amp may run out of puff, even the most powerful ones like the Denon X8500, if you continually run at high volume. That's why with a full speaker load you will find people adding power amps.