I don't think the XSL is a good match for these turntables. The XSL is a great cartridge, and a little bit fuller sounding than the older OC9s, but it's still on the lean side. Audio Technica carts are better suited to turntables with a bit of body, like the LP12 or Technics.
I don't think you'd find an Ortofon 2M much better. I had a 2M Black on my RP10 is similarly found it thin sounding. In my opinion, the 2M carts are more like AT carts than the older Ortofon ones.
The best match I tried on the RP10 was the Exact, which is hardly surprising I guess, but I still found the sound lacking in body. Like listening to cardboard cutouts instead of real artists. A lot of people seem perfectly happy with this sort of presentation but I'm not one of them. If you like the general presentation of the Planar8 I'd be looking at warmer cartridges, maybe Grado, Nagaoka, Hana perhaps? Or Rega of course. I love the Exact and I have an Ania Pro just now which is also very good.