Dolby Atmos is a significant change in design for surround. You would either need to add ceiling speakers or replace your speaker system with something like the Andruw Jones designed Atmos speakers from Pioneer Elite and that will run you around $2500.

I personally like Infinity Speakers though mine are a bit older than yours and a bit higher end. You can always buy higher end speakers. Infinity has always produced high quality speakers at a fair price. To outperform those, expect to spend $2000+ for a noticeable step forward.

The receiver you choose really comes down to a few variable. Cambridge and NAD make more musical AVRs. They include old versions of Audyssey in the lower end models and video processing is not a priority. Alternatively, they sound great for 2.1 stereo but have no really good features like AirPlay.

Marantz and Denon are more balanced. They include much more up to date versions of Audyssey, even in modestly priced units. They have all the nice features like Pandora and AirPlay that make the unit more functional and they sound very, very good.

Regarding Audyssey, the less optimally designed your room is or the less perfect your speaker placement is, the more important Audyssey and the latest version is. If you want to step up to Atmos, I wouldn't consider a device that doesn't have XT32.

I have a Denon receiver in my family room and have a Marantz Pre/Pro and Power Amp in my basement / theatre room. I have AirPlay and Pandora on both units and I use it all the time. I think they sound fantastic and wouldn't hesitate to recommend either to anyone. The Marantz AVRs have a touch of warmth that will work nicely with those Infinty speakers.

for instance the SR6007, SR6008 & SR6009 are the same model with steadily updated technology. The SR6007 can handle 3D, but can't handle copy protected 4K video. The SR6008 can handle copy protected 4K video and the SR6009 incorporated Dolby Atmos.

As far as audio is concerned, they are all about the same. You may see a slight tweak in Audyssey and I think the later units have wireless instead of requiring an Ethernet connection.

Alternatively, the SR5008, SR6008, SR7008 is a progression in features and power. The unit you should choose really depends on what you need. It you are thinking about upgrading to 4k TV or Atmos, then you need a Marantz unit ending in a 9. Do you need 2 or 3 zones? I use one of my receivers to power speakers on my deck in a zone 2. Do you need wireless or can you run an Ethernet cable.

If you don't need Atmos and you aren't planning on 4K TV, the SR7007 is an awesome value at like $899 out at Crutchfield. If you are planning on stepping up to 4K but don't care about Atmos, the SR6008 is probably the best value. The 5008 might also be fine, but it will have fewer features, etc... i don't know exactly what you are going to need.

I am not a huge fan of the NR units. They are light on power and are great for smaller rooms but in a bigger room, you should stick to the SR line.