If the Crutchfield harness is similar to the Metra, which should be the same for all late model Toyotas, then it won't be a problem.
I suggest spending an hour when you receive it to solder the harness wires to the D3's wires. Use heat shrink insulation if you can. The Crutchfield one will probably have the color codes listed for the wires. Simply match these with the wires on the D3. If the Crutchfield has two wires for illumination, use the one that is Orange/White. This should be the correct polarity or the Scion. The other one would will not be used.
I assume you'll be doing the bypass for the D3, so routing the parking brake sensor shouldn't be an issue for you.
The VSS (speed sense) wire is the purple one located on the same factory wiring harness as the steering wheel control wires. The reverse signal is located under the dash on the left of the steering wheel. Most wire locations can be found by following the factory navigation installation manual, which can be found at TRD Sparks
. These instructions are 90% applicable to any aftermarket nav unit. Also read the End All sticky
in the ICE forum.
This was all the information I needed to install the Z2 in my xB. Good luck.