I used to drive my X-CS with a 35 watt tube amp. I also used a 60 watt solid state amp, and even tried a 200 watt amp. All worked well. With more power you get a little more volume and better control over the drivers. But even the 35 watt amp drove them more than loud enough.
I also tried a 2.5 watt tube amp which worked but only at a low volume. If I turned up too much it would lose control and not sound good.