I'm not too worried about the warranty, the Apollo units appear to be well built and shipping them around the globe is impractical due to time and costs.
Either they work, or I will try to fix them (with lots of advice from helpful people like you and jstefanop no doubt).

However, for now the auxiliary fan contraption is not to be trusted. All original fans are still running unmodified.

One of the power supply fans has a 200 ohm trimpot soldered into the cables (that warranty is definitely toast!), but the trimpot is again turned down to zero ohm. I found out that 200 ohm makes hardly any difference to the speed and noise of the power supply fan. And that a Noctua fan of the same size appeared actually louder than the stock fan. So I sourced some 500 ohm and 1K ohm trimpots to experiment some more.

Using the current version of the auxiliary fan contraption would risk accidental turning off of the auxiliary fans by touching the switches. It's just for experimenting and for finding the best fans and resistors to physically reduce their speed and noise.

After I know which fans and resistors I want, I will use switches that have no 'OFF' position, only 'High' and 'Low', or no switches at all and will solder resistors rather than trimpots in series with the auxiliary fans. The slow setting will hopefully be sufficient to keep the Apollo safe even if the stock fans fail or are turned off, the high setting should have equal or better cooling results than the stock fans (ie keep the miner and Orange Pi at lower temperature than the stock fans would but with less noise).