Here's what I bought:
KT-STGH-95436 Kennedy Technology Group CellSet MC/GPS-Harley ($225)
KT-DX550-95423 Stereo Device/Mic Harness, Zumo 550 ($95)
The kit worked flawlessly. Took me about 2 hours total. No soldering is required; however, you do have to disassemble two multi-pin connectors, and applying heat-shrink tubing to wires the two plugs on the back of the radio. The instructions are crystal clear... just take it slowly, triple check everything as you go... and no issues. The company is small, extremely helpful, and they have a toll free number to assist you if needed.
I attached a few pics to help you see... in the last one, the black box is the actual cellset installed on top of the radio. As you can see, everything we VERY clearly labeled. If you've never dealt with Harley connectors... add another hour to the project. Also, if you go this way, you can gladly call me for info along the way... like some tips about making the connections.
Lastly, you can download the installation guide from: http://cyclegadgets.com/products/KT/detail.asp?SET=GPSH