Suggestions on Pre Amp/Amp or Integrated Amp

I’d look at Emotiva. 

Your budget could get separate processor and amp at 250 WPC five channels driven vs. 50 W shared in the Marantz.

Even their HT receivers are much more stout that the Marantz.

If the room acoustics are only ok, don't waste your money. Get the functions you need, including power, and give the rest away.

5K for mostly movies? Hasn't been invented yet. I would ask a home theater forum. This is a hifi board.

Yeah if it’s mostly for more power/better bass you could just get a more powerful stereo amp and hook it to the front L/R pre outs on the Marantz as the NR1510 is underpowered for your CM8s.  You have a decent sub, and if you haven’t already done so you might look into optimizing its settings/positioning to make sure you’re getting the most out of it.  If you have a large room you might also consider adding a second sub, which has many benefits.  Best of luck. 

Thank you all for your suggestions!