Should be a solid synth, as far as 4 voice poly analogs go. I am not super familiar with this particular guy, but Dave Smith is usually quite generous with his modulation matrix- lots of glorious potential for making complex sounds.
Here's where this synth falls short, and where it excels, just based on the specs, imo:
- Lack of individual outputs for each voice- ideally you would have the choice between a 4 voice analog synth, or 4 separate monophonic synths in one, each w/ a different midi channel in your DAW. Two oscillators per voice would have made this an attractive proposition. Not a deal breaker, but something that other synths have offered.
- Analog VCAs- can be good or bad, depending on the execution. The execution of the VCAs in the alesis andromeda was seen as a shortcoming in an otherwise incredibly synth. The recent Korg Minilogue 'clicking' debacle is another example. Just see what owners are saying about it first.
The filters should be great in the X4, at least.
If you are a big fan of Massive for making super agro demon sounds, I would also recommend you check out the Waldorf Q. Quite different than the X4, Its a digital wavetable synth. Very capable & very knobby with a full keyboard. The combo of FM, wavetables, ringmod makes it a very interesting piece of kit.
youtube.com/watch?v=wuHaguhynOM
I managed to get one for 1100 USD after camping ebay, which was a good price. Multiple outs per layer (can divide up the 16 voices into 4 separate layers with their own output or midi channel, or build a complex 4 layered multi patch where each layer has its own modulation).
Another even more oddball digital synth I would recommend is the Korg Z1. Truly a strange beast, physical modeling oscillators as well as the standard waves + FM makes for some truly alien shit. Its not very knobby, and requires lots of menu diving, unfortunately. But a damn fine synth that is underrated.
youtube.com/watch?v=mcNhJI92cF4