its better for a few reasons to have the wideband directly into the ECU.
The AEM does not accept an input, so the easiest option is to run 2 sensors.
I always try and talk my customers out of having a wideband gauge in the car. You are busy driving, not watching a gauge. Let the ecu do its job and review logs periodically to keep peace of mind.
Good that is my intention too. Seems the easiest way since there is already a LSU4.9 installed from the AEM, why no reuse it. Did you consider about adding GPS/G-sensor capabilities also btw ?