DIY Installing VAIS SL2I - How?

Hola. I've tried searching the forum, but either this question hasn't been answered or my search fu is weak. (Probably the latter.)

I just got a VAIS SL2I, and attempted to install it in my 2004 Prius, which has a single-disc CD player. Unfortunately, I couldn't figure out how to do it.

The SL2I unit came with two cables. A connecting cable that runs from the unit to a Y-shaped cable, and the Y-shaped cable which, according to the instructions, should plug into the "head unit" in my dashboard. I took my dashboard apart, but couldn't find any sockets that fit the smaller male plug on the Y-shaped cable. I assumed the "head unit" was the video display unit, which had three sockets in the back similar to the graphic in the (exceedingly vague) SL2I installation manual. However, none of those sockets matched any of the plugs on either of the SL2I's cables.

I also found an instructional PDF for installing VAIS' AIC-100i. I located the socket which that manual mentions, located on the back of the radio unit. That didn't match either.

Is there an explicit installation manual for the SL2I out there somewhere? Or, is this the kind of thing I absolutely need to go to an expert for?

Thanks in advance,
Conrad