Shadow priest is really insane in aoe, and a lot more powerfull than sham in singletarget with lot of group-healing, hymn are usefull too, so, i recommend spriest stacking for the dps part. I probably replace 2-3 more sham soon and keep only 1 or 2.
im managing dps like you, a macro for 1key rotation, basically i have 1 key for single target, 1 key for multiple target, and 1 key for aoe
With a single demolock replacement you can get easy +15/20% dps (+13% of element curse, +5% crit, and more spell power than wrath totem, that allow you to use the damaging fire totem on all shaman)
If you want to keep a shaman stacking, you have to aoe with totem, keep 1 wrath totem or a flametongue to boost the spell power of other and accept the low potential of shaman dps :(