Looking real closely through the darkness (
) it looks like it is. It should be the component behind the black mounting plate that has the large colorful wiring harness going to it right below your Nav CPU.
Here's another pic below (that illuminated a bit better) that shows the (MK4) Nav CPU, CD Changer, BlueTooth/TCU module (silver thing mounted at an angle), and the amp (located behind the BT module & black mounting plate):
(image courtesy of a thread at Xoutpost.com)
And since you have the 4.8is...I'm sure you probably have the DSP amp...which is #1 in the diagram below...and the component behind the BT/TCU module and mounting plate. The DSP amps have 3 wiring harnesses that connect at the top (the non DSP amp only has 2 harnesses that attach along the top):