If you're going to really crank 'em up, you may want the 2150's extra power. I've got the X-LS classics in my setup, as I think you've already noticed, and they have paired up nicely. With an X-Sub in the mix, having the 2150's bass management would be handy - I'd start out setting it at 80Hz, as 60Hz is a bit closer to the -3dB point of 55Hz than I'd like (although you could certainly try 60Hz, as well).