Actually listened this morning to my system with Magic Cubes installed; heavily modded Audio Van Alstine 250 wpc fet-valve amp (daikom filters on terminals), heavily modded air-tight tube preamp, Alesis ML 9600 Balanced power technology modded CD player/recorder, locally made copper cable interconnect and speaker cable (by automotive cable engineer), and Magnepan 1.7's with enacom speaker filters attached.
The addition of the Magic Cubes produced startling improvements in the air around instruments, the separation of instruments, the tone colors, dynamics, imaging (now extends clearly beyond the speakers) and increased the overall body of the music across the frequency spectrum. No frequency was accentuated. The changes overall were a very noticeable improvement to a fine sounding system. The system was just cleaner and clearer with a perceived lower noise floor.
I give the Magic Cubes very high marks. I have tried many, many tweeks. I have had good, bad, and everything in between. It is hard for me to imagine what you could do for your system of about 500 bucks that would get you close to what the Magic Cubes did in my system. It also seems to clearly provide incremental benefit to the other tweaks in my system.
I can't wait until they truly break in.