What's is this?
 

I pulled off my passenger side panel today to run my amp wire and found this http://i157.photobucket.com/albums/t...6/a82e9cca.jpg

What is this? I have had my panels off before but this is my firsttime noticing it. It runs to my antenna.

BCM maybe? I forgot where they mount them. If it was in the hatch area i woudl say amp for stereo, but hard to tell where exactly the pic is of. The monsoon system amp is mounted behind some stuff in the passenger hatch area.

That's about righ where the year seat goes behind the panel next to the floor. On the white sticker it says audio. I know it's not a monsoon amp as the car didnt cone with the monsoon system

If you have a pre monsoon 10 speaker sound system it's an amp. It powers your sail panel speakers.

+1 - yup that is the amp for pre-monsoon systems. Should be mounted right near the armrest behind the passside sail panel.

Do I still need it if I'm not using the stock head unit?

Yes. Any head unit regardless of whether it is stock or not will still power the amp if you are still using the stock harness.
If you have ran new speaker wire directly to a new head unit then no you would not need this amp.