crossfire of watercooled R9 on x79 extreme 9

[aksys]

Hi everybody.
I wish to install a crossfire of R9 290x, wattercooled, on
my x79 extreme 9 MB. Asrock user guide says that I must use
PCI slot 1 and 4 for a crossfire, but I wonder if the
sound blaster card in slot 3, witch is so close to slot 4,
will not interfere in the installation of 2 big watercooled
GPUs with backplates, becuz of the bigger thickness than
aircooled ones.
thanks