Hi,
You need to keep a few things in mind before purchasing the right set of speakers.
Firstly the impedance should be the same or more than the AVR / Amplifier, this will ensure minimal stress on the power section.
Secondly, you need to ensure that the speakers you select can perform across all frequencies between 20hz to 20khz. Typically Tower speakers starts from 35/40hz till 20-23khz. The maximum spectrum of frequencies provides, the better delivery.
Next is the cone size of the speakers. The bigger it is the better throw and frequencies emitted.
You need to check the output specs of the X1000 and accordingly purchase speakers which have the same output or more. Do not look at the peak power output.
Here are a few recommendations, Bostons and Wharfedale work well for music and movies. You may want to add a subwoofer later to get that depth and punch for movies and music.
Boston Acoustics A 250 Floorstanding Speaker
Boston Acoustics A 360 Floorstanding Speaker
Wharfedale DIAMOND 10.4
Sonodyne also has some good towers
Sonodyne Sonus 2605 V3 Floorstanding Loudspeaker
Sonodyne Sonus 2504 V3 Floorstanding Loudspeaker
There are other brands like Jamo or Yamaha or B&W in the market. It all depends on the size, what appeals to you in performance, quality etc. Polk has the RTi series which you may want to consider. The key is to audition as many towers as you can and if possible carry your AVR as ultimately you will be connecting the shortlisted selected towers to it. Also your decision is based on the fixed budget you have. Check with multiple dealers for the best price and warranty.
All the best, hope this helps.