I've got X-Sim running using the guides. The guides are for older versions of X-Sim so it's not easy.
It took me some time before I realised I had to press "Start" in X-Sim Converter before getting some output...

THAT part wasn't mentioned in the guides (OK, call me stupid

). Did you press Start, Paul33993...?
I recommend testing X-Sim using a headphone connected to the stereo output of your second soundcard (it's the green connector): you should hear the engine humming while driving. Output is sent to both left and right channels, so you can drive 2 shakers if you want (same signal though). Start with RPM effect only. Add 'gear change' later when the output is working. A note with the gear change effect: in the math setup, third step (in the lower left of the window) it should be set to 50% and "add result value" or else you will lose the RPM effect.
Also recommended: turn the treble on your amplifier down because I can hear a ticking noise in my headphones when the RPM is changing. By turning the treble down you can avoid this.
No idea yet what it
feels like since I'm waiting for my shakers to arrive...