Marco,
When I first saw your room pictures I was taken back by all the poly's (DAADs) so knew you were as serious about room acoustics as the great gear you've selected. Kudos. Like you, my dedicated basement music room is my man cave and is close to your dimensions: 13'8" * 21' * 7'. Looks like you're placing the DAADs at the corners, 25%, 33%, 50%, 66% and 75% points of the front wall's width. Do the DAADs offer one side that's absorptive while the other side is diffusive? What sides have you got facing into the room - I'll guess that it depends on the location of each DAAD. Hearing your strategy would be of interest to me. Are you using DAADs of various diameters so as not to overly 'correct' a narrow bandwidth?
I see in one pic what looks to be a 2nd pair of speakers in a glass enclosure?!? What are they?
Bet it sounds great. I too love the sound of tubes with efficient speakers and use the PX25 tube to good effect. Congrats on a great looking room and gear.