Any spindle will fit the XXL, but for the heavier ones (2.2kW) you will probably need to upgrade the Z axis (HDZ or similar), so if it’s only to benefit from the lower runout, an 800W spindle would be best suited (similar weight and diameter as the routers, works with stock Z axis). There are a gazillion threads on the forum about spindles, this one is probably my favorite.
But don’t go there, you’ll get gear lust as I did 