To clarify - I've secured my fan to the outside of the power supply cover, blowing air into the the power supply through the "grill" of holes that exist in the psu cover side alongside the rom and ram slots in my e5000 and then I 've masked the remaining holes ie air from the main space of the sampler is forced into the space under the psu cover. My concern about this method was the psu cover looks like the ideal resonant form with it's thin metal and large area, but thankfully it doesn't seem to add up to a loud volume. I'm relying on pressure within the psu cover to exhaust the hot air rather than blowing air in the direction of the rear exhaust apeture. I'm not sure which method would be the most effective but I know at least as much air comes out now as did with the 40mm fan. I'll post images when I can.
Looking at your images Andy the grill I've fitted the fan to is the one in the bottom left hand corner of your motherboard photo next to the sticker that says no servicable parts or "Keep Out High Voltage"