OP,
Very good move. I moved my system along in similar fashion. You want a great streamer. I recommend a Aurender N100. It is what I use to drive my headphone system (see my UserID). You are in for a treat. I also have Sennheiser HD800… and some other high end headphones. You are in for for a treat. Get a good streamer… don’t go budget. Match your streamer quality with the rest of your equipment.