Hi Realremo, you have a sweet looking system setup and room. Totally agree with others about acoustic treatments and speaker placement. These are no-brainers.
Moving on from there, I'm looking at your source as the next candidate, cause there are certainly lots of options to improve fidelity.
I was also looking at the Small Green Computer CAPS-based solutions to replace my current Squeezebox Touch front-end. Digital source does really make a difference to end sound quality. USB, SPDIF, jitter, power supply and computer noise still require lots of effort to combat. But looking at the cost and ergonomics, you may also be interested in the upcoming Auralic Aries streamer. It seems really cost-effective and looks preferable to me to having a CAPS.