I've got the polk dxi650s shallow mounts with stock non infinity head unit. They're way better than it was stock. Poly fil helped too. They really brought my sound bar to life. I can't speak for upgrades to the infinity system, but just adding the polks to the sound bar made a difference to the stock system. Granted, some 2 ohms could have helped more, but from my experience, the polks are more than enough for the soundbar.
I'm now adding a jl 700/5 amp, focal 165 component fronts, and a jl 8" sub to fill out the sound some more.