Well after months of construction I finally unboxed my EP350 and noticed that I the back control plate is identical to that of the EP500!
I didn't know anything was out of the ordinary because I had gone through the user guide packaged with my 350 and the diagram of the back controls were all listed.
It was only when I went to look up the user guide for the 350 on Axiom's site did I notice that it doesn't have the USB port and Trim knob listed!
In looking at the user guide for the EP500, I noticed that the diagram of controls is identical to what is installed on my EP350!
Now I've discovered this thread, but I'm at work so I cannot pull the grill to check the driver or view the included user guide to make sure it says EP350, but it looks as though I was able to obtain an update/hybrid EP350 from the Factory Outlet Store!
...I shall call it "Franken-Woofer"!