Suggestions on Pre Amp/Amp or Integrated Amp

IF it was me, I would

1. pick an integrated amp with pre-in or ht bypass

2. use it with the existing Marantz (unless you really don't like it)

because, that will work with the existing Marantz for Video 5.1, and sets you up for separate and better power for the front L & R, better for them, and lessens the load on the Marantz, or any future AVR.

and, is ready for other 2 channel sources, like streaming, cd, even vinyl if you have the room for it and inclination

keep in mind, this is what you would/should do even if you buy a new AVR (with front pre-out)

Primare SPA25 will do the trick for a bit more money.  Anthem or Marantz would be my other two considerations in this price range.  Stay away from emotiva.  I had 300 wpc emotiva amp and it's sound was easily bested by a 30 yr old NAD class AB amp.  The sound from the primare is very, very good where she, you should be satisfied.  You can always add a class AB to the marantz or anthem down the line for the front channels if you become dissatisfied.  I ended up replacing the emotive with a pair of van alstine monos.

A new AVR powerful enough is certainly a solution, that's what you asked for, just make sure it has Front Pre-Outs for future options.

While looking in the past, I found:

Certain brands (I forget which) generally have front pre-outs, like your existing Marantz, while others, even their top models, may not have front pre-out.

They often do not tell you in the literature, it may show up in the specs, I find the quickest way is to find a photo of the rear jacks, look while magnified, see if there are pre-out jacks, and see if front L and front R are there.