Re: What vice for a Sieg X2?
Measure the width of the table, double it, and that is the total overall length of the vice you need. You have half of it hanging over the front of the table. In your case somewhere about 184mm long.
If it comes with a detachable swivel base, take that off before fitting, as all it does is reduce the rigidity of your setup.
The 80mm one of the first ones shown should be ideal. I wouldn't recommend the very last ones.
http://www.arceurotrade.co.uk/Catalo.../Machine-Vices
All you would need to do is to make some hold down clamps.
Bogs