I have a 2012 Audi S4 with the 3.0L supercharged V6 that I want to do the carbon cleaning on. Besides the walnut blasting to clean the tops of the valves, what can be done to clean the inside of the cylinders?

the TL;DR part:
The car actually drives just fine but I want to tune it. I was doing some logging while stock and saw some adaptation knock timing pull. If I didn't log the car I would never have known this even existed as the car pulls hard. The tuner suggested that carbon buildup in the combustion chamber might be to blame. I tried to get a look down in the cylinders with a borescope and for sure there is carbon there (what engine wouldn't have carbon?) but I can't tell how bad it really is...it wasn't the best scope and I didn't have the tool to rotate the crank to get the pistons to the bottom of their stroke to get a really good look. And honestly I don't know how bad, bad looks.

So I plan to do the walnut blasting but I highly doubt this will solve the issue so I was looking at doing some sort of chemical treatment to get inside the cylinders if that is even a thing. Still waiting on the dealership to get back to me on what they could possibly do. I find it hard to believe that I am the only one with this issue. The car has all fresh plugs and coils, pulley's tensioners, water pump, oil, coolant. I can't find anything that might be causing "false knock" but of course it must be very subtle. I also have run 2 tanks with BG 44K cleaner through and no noticeable improvement. I also run either Shell 91 or Husky 94. The timing pull on the 94 is much better.

Any suggestions would be appreciated.