I have pimped up the Apollo with lots of heatsinks to reduce the noise further (fan runs below 1620rpm at 30 degrees C ambient) and I run it without the case. As a minimum I suggest adding a heatsink to the R44 power converter at it is quite hot (>60 degrees C).
https://imgur.com/a/SB6A4puI use the following heatsinks:
20 off 20x20x10mm
11 off 8x30x8mm
2 off 6x4x4mm
1 off 14x14x5mm
The 8x30x8mm heatsinks probably help cool the Apollo down the most as they are at the base of the main heatsink.
Smaller 20x20x5mm heatsinks would probably work just as well and be cheaper at the top of the main heatsink by the fan.