I have been using a BLOK system for some time now.It's very sturdy and you can mix and match the shelf spacings when you assemble it.
Perhaps it's main attributes are that it not only houses whatever you want to put on it but also if you ignore the cable holes at the back of each shelf, the side pieces are thick enough to run cables down the back out of sight with power one side and signal the other.
Even more important than any of the above is the fact that my wife thought it looked great.Not often you can get brownie points in connection with HI-FI.