IDE "Controllers" can have 2 devices, a Master and a Slave; the ACard is a "Bridge" or a conversion device, not a controller.
That's what I was thinking, using the ACard as a bridge to a controller that supported two cards. Wonder if it would work? Yeah, probably not. I wouldn't be surprised if some enterprising Amiga user tries it out though!

Edit: Does the Amiga even recognize when there's an ACard plugged in? I would think it would be invisible to the system, the Amiga would just see the device at the end of the chain?