Some handy things about the powered spawner: by default it behaves as a spawner and I don't think you get much control over where the mobs spawn. If you want to build an easy grinder then you might try running it in "capture" mode instead.
In capture mode you supply an empty soul vial and it puts the mob in the vial instead of spawning it. This combines quite well with the autonomous activator. Using the activator gives you precise control over where the mob appears.
In the picture the spawner is configured with its "pull" side facing the spawner, this saves you having to configure a servo and/or filter. The push side outputs into itemduct. In this example I've used fluctuating itemduct so it also supplies power.
ONLY PUT IN ONE VIAL, if the filled vials stack they cannot be right-clicked meaning the activator will jam.
As far as I can tell the autonomous activator will not auto-eject. It doesn't appear to recognise the augment.
If the COFH wiki is right it might be possible to put the spawner next to an unmarked
side of the activator and set the spawner to push and pull directly, eliminating the need for the duct, but I could not get that to work.