Recommendations Amp, DAC for Kef R900

Looking for advice on Amp’s and DAC’s for my new Kef R900 speakers.  Currently running them with only a Yamaha A-S801 amp, and I’m afraid I may be under powering the speakers, and may damage them (although I have not heard any clipping yet).

I am using a Sonos Connect - listen to mostly Tidal and Spotify, both through my iPhone, and the USB port on amp.  Listen to large variety of music, but mostly to Alternative, Classic Rock, and Reggae.  I will also be attaching TV to system soon, but will use the system 99% of the time for just music. Unless I start watching a lot of movies, I don’t plan on adding a sub. Have the system setup in my fairly large, basement. 

I want to purchase a very nice system, but only want to purchase in steps.  When finished I would like a good 2ch integrated Amp, and DAC system, but am wondering if I should get separate Amp/Pe-Amp.  Would I notice a big difference listening to streaming?  I was hoping to use the Yamaha as the Pre-Amp, and buy a nice Amp next, but I believe that this is not an option.  I want to buy used, budget of $2k for Amp, $1.5k for DAC, but I am flexible.