Hard to replace the heatsinks on those. It's all connected as one big heatsink. Try getting something like an Antec spotcool fan and blow on the largest finned area.
Or, on the very high end you could get a full cover waterblock setup for it. Blocks ohh $200, rad, $50, pump $70. Might as well do the CPU then too and toss the GPUs in there too.
Actually, don't forget linx is just a benchmarking stress tool. Under normal use you won't be seeing those temps.