I have to agree the Q7 basic to colour MMI is not the easiest upgrade or the cheapest. I have done several and they take a long time. Basically the issue is with the amplification. The Basic Q7 does not have a seperate amp like in the A6 basic. It is built into the CD player in the dash and the car only has 8 speakers.
So when you upgrade to MMI high, you need a sound system which then has a requirement of front dash and center speakers and a rewire of the doors to split the BASS and TWEETERS speakers apart and link the TWEETERS with the dash MID RANGE speakers. All very time consuming and complicated as the AMP locates to the boot along with the radio. So again lots of rewiring and running of fiber cables as the boot does not have any fiber for the MMI.
There are so many things to fix in the Q7 from 2G basic to 2G high that it really is not worth doing.
I would suggest an MMI 3G upgrade as a better option. Less components to swap and cables to run. You can probably get away with mounting the radio/amp module under the armrest where the AMI would have gone in a 2G system. A lot less wiring, but would require a can gateway to make the cluster work, if indeed it will display on a red cluster which I'm guessing you have in a basic Q7. You would also get bluetooth and an Ipod/USB (AMI interface) for the money.
So for MMI 3G you would need roughly the following.
MMI 3G 5F unit for a Q7 (high or low, what ever your pocket can take)
MMI 3G radio/amp
Can gateway with new software to support 3G (pig to change as it's way up the dash below the air outlets)
MMI 3G control panel (high or low, again depends on what you want)
MMI 3G screen and cable (high or low) and screen surround to suit. (Maybe some new buttons for the screen surround)
AMI cradle bits and pieces to hold the radio securely.
Some FAKRA extension cables and plugs and sockets to fit the 5F unit and radio.
Front speakers for the dash and screws to fit them.
A GPS antenna.
A much better system if you go for the MMI 3G high. I converted my 2007 Q7 from 2G to 3G high and it was well worth it.