I totally understand. I haven't owned either speaker, so I can't speak from experience, but I believe the XD has a powered subwoofer section. That said, you can expect an increase in midrange and high frequency resolution as your main amp doesn't have to work so hard to power the entire speaker. This isn't just a modest increase. It is quite noticeable and worth the extra cost. I did this with my system adding a powered subwoofer with the same dramatic results. Just my opinion though. Others may contest the increase.
Cheers
Tim
Cheers
Tim