There are a whole lot of issues here. And in my current condition I am likely going to poop out before I can type it all out...

1) The only numbers on the Pantone website that mean much for the representation onscreen of spot colors are the RGB values, for obvious reasons...it's what are monitors use and is in a wider gamut than CMYK.
2) The CMYK numbers on the Pantone website are "uncharacterized" numbers. In other words, they are "dumb" values that mean, well, nothing. They are number values without being transformed by any CMYK color space both as regards a CMYK working color space and/or an ouput color profile.
3) Xara has no ability for having/using a CMYK document color space. I have long asked that LittleCMS be integrated. It isn't and likely will never be though it is an OpenSource color management system.
3) Xara only transforms Pantone and/or colors to an output profile in the case of PDFs. It uses, by default, a rather generic profile by default but the color values when working with CMYK are transferred to a PDF accurately.
4) The proper Pantone numbers use LAB values to characterize the colorants. This color model is the only accurate model that can then transforms the color values both for onscreen using a document color profile in conjunction with an output color model.
5) Xara applications cannot use LAB color values.
6) LAB values for spot color is what all professional applications use.
7) Pantone or other spot colors as characterized in Xara applications are only viable when actually using them as spot colors in a PDF and for printing professionally as spot color. However, that said, any print establishment worth a hoot can, using most any RIP or Acrobat, transform the spot color itself to CMYK values as accurately as any Adobe desktop application from the start.
8) The Pantone LAB values in say AI will vary when converted to CMYK depending upon the document CMYK working space. So using 3145C in conjunction with US SWOP as the document color space, the LAB 3145C swatch is transformed the CMYK values of 100,35.77,38.11,7.5, well different to the dumb numbers on the Pantone website.
9) Nearly every consumer desktop printer I am aware of convert CMYK, well all color values in whatever color space, to RGB inside the print driver and then convert again to CMYK inside the printer's RIP. There are exceptions as to what happens to inkjets with more than 4 inks as to what happens in both the print driver and the internal RIPs. There are also exceptions as regards higher-end PostScript consumer printers as well--some do have CMYK print drivers, for instance as well as some also have Pantone look-up tables.

my arm is getting fatigued and so i'm done for now...