Hi. I'm a South African currently living in Oz but speant the last 2 years in Copenhagen. I must say, your public library system is the best in the world, with a bigger music selection than any record store I've ever been in. I ripped about 400 cd while I was there, bless them. Funilly enough I store them exactly as you do, in boxes on the floor with alphabetical cardboard dividers seperating the plastic sleeves. Easy to transport that way.
Dont know what I could advise, other than obviously treating first relection points on side walls, floor and ceiling. DIY bass traps are also hugely beneficial. Re rack, I think its better as is, or on a granite slate, rather that having them raised if they are to stay between the speakers. Will mess with imiging a bit otherwise. cheers
B.