I think this setup fails in design. the first turbo is simply in the way of making power. The compressor side is fine. Its the exhaust side that will not work like you hope. The 16g will overspin and die very quickly, the second turbo will not recieve enough exhaust energy through that small wastegate Compound turbo setups work well on diesels where they should stay. Diesels tolerate very high boost pressures because the engine itself runs off autoignition point of fuel/air charge.
The AMS design staged twin turbo was brilliant by design compared to this setup. They only had a few days to get car ready for event . they feared they wouldnt have enough time to work out bugs so they had to abandon the project.
I cant find pictures of that but a quick search found this new 1.9tdi with staged chargers
Fiat Powertrain: 1.9 JTD Twin Stage Turbo with 100 hp/liter