I have a '17 VW GTI Sport. 3600 miles so far. It comes with a lot of nice features but the stock sound system is very average. So I upgraded. The product I chose is best described here
http://www.audison.eu/index.php?page=product&id=76 I first heard of them when I contacted my local car audio retailer and asked for their suggestion. At the time I was considering the Helix upgrade. In short. if you have a Mk 7 Golf that did not come with the Fender or best available sound system, this is meant to replace the OEM front door speakers and adds an amp with DSP and a subwoofer that fits nicely in the trunk without interfering with the spare. Some would likely say this set-up properly installed is superior to the Fender system in the 2017 Autobahn Edition Golf-I have not compared them. Once installed, it is 100% seamless by which I mean that there is no visible change whatsoever-OEM head unit remains unperturbed and no change to the trunk visible from the hatch. Audison offers replacement tweeters but also recommends keeping the factory tweeters as they apparently do their job quite well. It does not come cheap-I paid $2,250. The kit itself sells for $1800 with the bass enclosure and I paid about $320 for the labor. It took the shop two days to get it done-into them last Thursday and out Friday afternoon-my guess is that the tech really spent about four hours installing it.The amp has eight DSP factory pre-sets based on type of music and driver position, and offers customization for those that want to toy around with or tweak the adjustments. Mine was set to "Position 8" which is said to be best for acoustic/rock and to equally suit driver and front seat passenger. My installer offered as part of the deal to tweak the settings at any time if I think it needs adjustment. Before I get to the sound so far, about me-I just bought my new '17 GTI Sport a month ago. I know little about car audio but a lot about home audio, a hobby of mine over the last 25 years. I have a home system that would be considered high-end by the most selective of audiophiles- built around Audio Research tube amp/preamps, OK, now finally-my thoughts so far. The difference is not subtle. I did not think the factory system in the '17 GTI Sport was bad-it was fairly good but lacked the degree of clarity I am used to at home and lacked deep bass. Even the factory midrange pales in comparison to the Audison set-up. Now, everything sounds more forceful without sounding loud. The midrange and bass are much improved as one would expect with upgraded front door speakers, wattage (allegedly 300, but pay no attention to billed wattage for reasons I will skip here), and a fairly large subwoofer. This is likely because there is far less distortion-loudness often is perceived due to distortion. So far I have primarily relied on CD's. I have also used my iPhone 7 with Amazon Prime Music-which has surprisingly good sound quality-hooked up via USB to Apple Lightning-and I use an Audioquest Jitterbug at the console end (USB device to reduce jitter). I have only six or seven hours on the new sound system. I have no complaints-the OEM system on a 1-10 scale was a 6 and now it's at least an 8, maybe an 8.5. Is it worth the high price? Worth nearly 10% of the price of the entire car? Those are really hard questions. I am a cheapskate at heart and for now would honestly answer "probably not". I hope to own this car for a long time and I do listen to a lot of music.