I don't know those speakers, but the beauty of buying an AVR like the X4000 is if you decided you did need a separate amp, it has pre-outs and will make a great pre-amp! IOW, there is no real risk of getting stuck with something that will not work.
In the American market, I would lean towards the X4100W because the difference in price is not much and the 4100W offers wi-fi and a few other upgrades.
On the other hand, if you know you will not use dual subs, you can drop to the 3000 series. Just make sure you have pre-outs in case you believe the amplification is wanting. ADTG seems to have a pretty good handle on the Denon AVR's (which I would recommend as well) and can point out which represent the better values.
Unless he was in a small room and you are in a significantly larger one, you should not need more power than ADTG had.