I successfully installed a Clarion CX501 into my VDC with a McIntosh system. I kept the existing amplifier and speakers.
Things I needed:
1) Phillips screwdriver
2) 1/4" socket with phillips head in it to reach a hard to reach screw, also maybe a 1/4" drive small socket wrench would help.
3) Metra 70-8901 Wiring Harness. This is missing the variable dimmer wire, but since the Clarion doesn't use it, that's fine
4) Needle nose pliers to grab the screws and clips that inevitably fell down
5) If your head unit is single DIN then you need Metra 98-8999. Since this Clarion is double-DIN, I didn't need it
6) Soldering iron, solder, and electrical tape
7) A Kenwood CA-SD200 Adapter, cut in half (we only need the circular DIN female end). Some of the wires seemed a little small and I was concerned at first, but since they are just carrying line levels, it worked out fine. This connector also has a shield around it, which may be beneficial for noise
8) A male to male stereo RCA cable, with the ends cut off at about 3 inches
9) Optional: A Bullet Splice Kit, 16-14 AWG (blue), 0.156" tab-male. We only need two of this package of 20. I bought Gardner-Bender Item # 20-163M at the neighborhood OSH. This is so that I would not have to cut the female plugs off of the wiring harness that comes with the head unit (Amp remote turn on, and Antenna Power).
Making the Wiring harness:
The Kenwood adapter has the following pinout:
1: purple, 2:large brown, 3: large red, 4: green, 5: yellow, 6: shields to both grey wires, 7: white, 8: grey center (red), 9: small grey, 10: blue, 11: orange, 12: grey center (white), 13: small red. The small brown wire is not connected.
I connected pins 2,4,6,8,12,13 of the Kenwoood adapter to each other, or large brown, green, both grey wire shield and centers, and small red. To this I connected all four shield from the RCA cables. I then connected the centers of the RCA cables to pins 1-purple-front left (+), 3-large red-front right (+), 7-white-rear left (+), and 11-orange-rear right (+). Pin 5-yellow is connected to the Amp turn on plug of the Clarion (blue/white). I then connected the Subaru wiring harness to the Clarion wiring harness, red to red (switched power), blue to blue (antenna power), orange to orange white (Illumination), and yellow to yellow (memory backup). The black wire from the head unit was attached to one of the screws in the Subaru that already had a wire grounded to it from something else.
I used the info from here as to how to wire up the RCA jacks (last comment by cj):
Removing the old head unit:
1) Remove gear shift trim (around shifter). Pry up on the bottom just a little (enough to separate the four metal retaining clips) and then pull straight back. There are a couple plastic pins on the upper part, one of which I broke because I lifted the base too high before pulling backwards.
2) Remove the two screws from the coin tray, set aside
3) Remove ashtray the two screws on top of where the ashtray was. The left one was a bit difficult to get to. Also, these use metal clips to secure the other end of the screws. Try not to dislodge them as they were a pain to get back in the proper place when reassembling.
4) Remove main trim-panel. Gently pull on the bottom part first, then work your way up. Disconnect the cigarette lighter harness when it becomes reachable.
5) Remove the six screws holding the whole assembly in (two to the left/right, and two below)
6) Remove the four screws attaching the climate control unit. The left ones were hard to get to and I used a small socket wrench. I think these screws are not pointed like the others, although I didn't realize they were different until reinstalling. They pointed ones didn't fit here well, but they did everywhere else.
7) Remove assembly, remove old head unit, install new head unit (same holes but use the screws that come with the new head unit)
8) Connect new wiring harness and test radio. Don't forget ground wire.
9) Reassemble in reverse order.
10) Enjoy great sounds
The total process took about 5 hours. The final quality was MUCH better than the tape adapter that I was using before. Hopefully I can sell the working McIntosh head unit for as much as I bought the Clarion for. There is small amount of high pitched engine noise, but it seems to occur only in acceleration. It is less noise than the McIntosh that it replaced.