get some cheap thin cable ties, pull cables to the outside of the drive cage and cable tie the cables to the holes on the drive cage (so the cables are between the drive cage and the side panel). this would drastically improve air flow through case. if you can use the holes at the front of the case all the better but if the cables are to short to stretch you may have to pull out a drive or two and use the ones towards the middle of the case, before replacing the drives. i'd also use a fair few cable ties on the ribbon cables to get them looking more like round ones as ribbons are notorious for wrecking air flow.
This looks like the best advice, although you could try folding the IDE cables.
For the ATX power, can you run it along the side of the PSU casing and down the side of the rear fans?