Hi Ludo,
You can run a lot off the Aquaero however I would suggest using the waterblock that is available to keep the fan amp temps under control. Using the waterblock, I have run 2xD5s and 8x140mm fans off the Aquaero without any problems or overheating. I think you could run even more but just check the power rating of your fans to make sure you won't be exceeding the Aquaero's wattage per channel. There is a review of the Aquaero here
http://martinsliquidlab.org/2011/12/20/a…view-guide-wip/ that tests how far you can push the device with fans and pumps attached and you can get a good idea of what can be achieved.
I think the new AC D5s were designed to be run directly off the PSU and controlled/monitored via the aquabus in order to reduce the pump's heat output. The speed is controlled via the aquabus rather than through a voltage regulator. I've ordered a couple but haven't received them yet so I can't tell you much from experience.
The PA2s can be daisy chained and I've read elsewhere on this forum that you can use a splitter to give you more aquabus connections.
Hope this helps a little.