Hugos,the high ceiling is a big benefit.When I bought my Avalon Ascent MK-2's I had a dedicated room built,literally to match the speaker energy projection.Only 8 ft ceiling,though.Due to construction costs.I had been advised by Avalon,on the dimensions,so it worked out great.It took me a couple of years to get it right.I have a large collection of original label Decca,Emi,Mercury,and Rca lp's.Along wiyh many other labels.I designed the room to allow for built in record shelves along the sides.This gave me good diffraction properties.I,then experimented(it helps that I have some very experienced audio friends)with various accoustical treatments.Remember,before the Osiris,the Ascent was Avalon's premier design,and are really an incredible speaker,but not designed for too large a room.I knew this and have been very careful with ancillaries(Rowland/Audio Research,all highly modified,btw),as well as careful room treatment.
You will have to be EVEN MORE conscious of your room's characteristics,as you will be generating much more energy,than me.I see no reason for it to be anything less than superb in low frequency energy,contrary to what was previously stated,with alot of care.This IS important,and cannot be overemphasized!!I'll try to be specific,since you have asked for the advice,but don't take my word as final.You must experiment,and research what is involved in proper room acoustics.You do not have to hire an outside service,for this,as careful personal comparisons are really all you need.As long as you aren't impatient.
Also--DO NOT treat the ceilings with any damping material.I have tried this,a few times.Once at the recommendation of a well known audio reviewer,who I knew,and it closed down the sound.DO treat the side wall area,depending on room width,with either something like energy absorption,or diffraction.Trial and error will come into play,but you WILL be rewarded.
Hugos,I have my equipment(as stated Rowland 8t,two chasis model,with second chasis upgraded from bettery to switch mode power supply,Audio Research Pre/phono,Levinson CD,SOTA table with Graham arm/Transfiguration,and good cabling)situated behind my equipment,like you do.This gives some degree of diffraction,and I have a narrow thin rug type awning above the equipment,in area behind speakers.I,also have corner tube traps,behind speakers,in corners.NOT TOO wide tube traps,as I had to experiment here.I have some 1/2 round, 5 foot tube traps mounted on wall to the side of the speakers,actually just behind where cabinet ends.Behind my listening area is a bay window,treated with a long absorptive(not alot)shade.To the side of my ear area is some flat Tube trap panels.I have small corner tunes,in area behind,and above speakers,along with a couple of flat absorptive panels.All carefully experimented with.
Oh yeah,I have carpeting in the room,and have mentioned that I use a REL Stentor sub bass system(behind right speaker)that is crossed over at 24 hz,and is set with VERY low gain,so as not to impede the Avalons' soundstage.
That should give you an idea of what I have done,which is NOT your room,obviously,yet maybe you can get something out of it.Obviously I'm supremely happy,but I've spent years modifying almost every piece of equipment,as well as the room.
The other things to cover,again,is bring the Osiris WAY out into room,if you want to hear them really breathe.They are almost like an omni directional speaker,they are so open,when set up right.Little adjustments can be BIG!!!
Also,please don't get mad---but, the what looks like a beautiful marble,on wall,behind system will most likely HAVE to be treated,if you want to hear what your current stuff can really do.Particularly with the Osiris in system.I hope you have an understanding wife,here!That's one reason I built a room.
Well that's about it,for now.I really wish you the best of luck!Keep us posted!!
