Are they 80mm fans?
I know with PC fans, the larger you get, the more cfm the fan generates, at lower speed
So if they use 80mm fan
Maybe you can get 140mm fans
Try to google the model of the OEM fans, and find out what cfm they put out
Then try to find a larger fan that has similar cfm
The other benefit of larger fan that runs slower is it draws less amps
So there is a power benefit there too
Another thing to test, is with pieces of cardboard
To try to direct the most airflow straight through the heat sinks
So you want to put a piece of cardboard on either side of the fan, and direct all the air through the heat sink
Keep it for a few minutes and monitor the temp on the software
If it goes down you can use the transparent sheets they use for overhead projectors instead
Because I don't recommend using cardboard that's flammable