I would suggest adding some Be Quiet fans and running at a low rpm, but if thats too loud just have one intake and one out take at lowest rpm as possible.
The silent pc worked perfectly without fans. Before the rebuild in May it was running for 1,5 years as mentioned, very little dust had accumilated. Because of the convection there is airflow in the case. The Antec Lan Boy Air is mostly holes so airflow has little resistance.
I have some Noctua A14 ULNs, and before I built the silent PC I found that Two of those with ULN adaptors was making a racket. I have taken a small break in my music production, that is why I rebuilt it into a gaming setup, but I am going to sell the GTX 980ti, build a small file server for the money, and rebuild my workstation into silent mode to work with audio again.