It took me literally about 30 minutes to remove, install, and replace all the parts, the worst and the longest part for me was taking the plug off the XM plug and plug it into the y-cable. Other than that, everything went smoothly.
Your second question...No, it doesn't affect your in-dash 6-disc changer's abilities. What the adaptor does is that it makes the HU think it's a separate CD changer so that's why it doesn't affect the in-dash changer's functions. For me, using the steering wheel controls trying to change modes takes a long time because it's got so many sources it had to go through.
