Before buying the Anthem STR integrated amp, you should know that Anthem also makes the STR preamp, which has a more sophisticated ability to independently integrate not only one, but two subs with ARC correction and also use them when you are doing home theater. So, you may not even need the Y splitting for your subs.
You already have a power amp for the front L/R channels, so I'm not sure why you would need the STR Integrated amp at all.
I'm not sure the STR Integrated will drive your front L/R speakers any better than your 200 wpc Rotel.
As to the speakers, I'm a sucker for big floor standers, so I would be all over the Amati's if I could swing it!