I've never found the XA160.5 to run out of power driving any speaker. Current capability is often more important than wattage ratings and the XA160.5 can output as much current (36 amps) as the X600.5. That's enormous.
Once you're talking about the big Pass mono blocks, the usual tradeoff of class A vs efficiency becomes more moot. The big XA.5s can drive huge loads and the big X.5s have enough bias current where the class A advantage is in a diminishing return territory. Here, personal preferences should prevail as the two lines are voiced slightly differently.
In the smaller Pass amps the tradeoff is more acute because you really can run out of power with the small XA.5s! (depending on what your drive, your music and room)
Once you're talking about the big Pass mono blocks, the usual tradeoff of class A vs efficiency becomes more moot. The big XA.5s can drive huge loads and the big X.5s have enough bias current where the class A advantage is in a diminishing return territory. Here, personal preferences should prevail as the two lines are voiced slightly differently.
In the smaller Pass amps the tradeoff is more acute because you really can run out of power with the small XA.5s! (depending on what your drive, your music and room)