I think that your biggest problem is this that Xara EPS didnt support Pantone/Spot colors

Maybe right decision is export like PDF, PDF from Xtreme PRO suport correct pantone/Spot colors..

On my ex-work I printed on one Muthon Rockhoper 2 - 64" and RIP worked very well with PDFs

RIP was some PRO version on Onyx or something like this... If I remeber well price of update to PRO was something like 4000 Euros....