IMHO, there's close to a 0% chance this is true.
There's a LOT of tuned N54 owners on this forum and I don't see a 'blown engine' thread.
For context, check out the RX8club.com forum. The Renesis rotary has close to a 100% failure rate with aftermarket turbos (ask me how I know
). You won't have any problems finding myriad tales of woe on blown engines there, trust me.
...not seeing it here, and folks have been running tunes for 3+ years.
Also, there's dynos of 500+ WHP on race gas & upgraded turbos. If the engine was 'at the ragged edge' doing 300 at the shaft, we'd be popping left and right at 400 WHP and wouldn't even be able to touch 500 wheel w/o 'that horrible sound'.