Seeking advice. Integrating surround with a stereo system

First thanks for reading. If you have some opinion about this subject then leave a comment.

Let me set the scene:

• Marantz AV8805 surround processor.
  
• 2 x Emotiva XPA-5 gen.3
  
• a homebuilt 20w power amp. for one of the dolby atmos channels. 
  
• some very good speaker in a 7.4.1 setup
  
• Tidal streaming with HEOS on a iPad.
• PS3 for Blu-ray
• LG 65C8 OLED
• PS Audio Detect
• Room treatment with absorbers and diffuseres. Carpet on the floor and heavy drapes.

My goal is simple, getting better sound. But how? Where should I start.
I have been thinking of buying a PrimaLuna integrated amp. But If I buy the amp I will also need to buy a streamer and a DAC plus interconnectors and some speaker cables. This is too much to buy at once.

Some options:

• The PrimaLuna has passthrough so I could use the Marantz as a pre-amplifier and start there.
• I could start with a streamer. https://www.allo.com/sparky/digione-signature-player.html
• Buy a really good DAC. The DAC in the Marantz is pretty good. So this is going to be expensive.

What do you think?