Going through the presets, I get the impression that all of them are monophonic. Can someone confirm that this is indeed the case?
I appreciate that some of the sounds are rather complex and maybe don’t need to be polyphonic, but other presets, would I think sound good as mighty multi-layered chords. What do you think?
It says on their website that X-Stream is a monophonic synth. Which, for a synth that is especially great for creating pads, I find to be a massive letdown. 
I missed that it had said that! Just as well it was free then 
It turns out that this is easily solved in Bitwig. You can stack instances of instruments in an “Instrument Selector” device and set the mode to “Free Voice”
Yes, you can apply this workaround if you’re a Bitwig user, but it’s a very cumbersome and time consuming workaround because for every change you make in one instance of X-Stream you have to go and apply that change in every other instance of X-Stream you loaded in the Instrument Selector. So, if for example you load 8 instances in order to have an 8-voice X-Stream and you tweak some parameters in one of the instances then you have to go and tweak the same parameters in each of those other 7 instances (or you have to copy this instance and paste it in all the other 7 slots of the Instrument Selector every time you make some changes) and as I said, this is quite cumbersome and time consuming.
It’s lucky that I will not likely need more than 3 instances of X-Stream since the individual sounds are so complex. And, in any case, the workflow for changing a preset is quite straight forward. Delete all but one instance of X-Stream, change the preset, then Cmd-C, Cmd-V a couple of times to create new copies of X-Stream. I’ve tried it and it isn’t cumbersome or time-consuming at all 
Maybe it helps to use the stack mode in X-Stream? You can change the interval of each pitch.
These parameters can also be automated.
You can also add additional layers to a patch…
…and load up to 16 instances of X-Stream.
Maybe these possibilities allow a way to create a polyphonic synth.
Interesting! I’ll check that out. Thanks for the heads up 
