DIY Audio Rack [*fail*]

Seen a few discussions on this topic and wanted to chime in with my experience. A recent amp upgrade necessitated a change from the "Solid Steel" rack I was using. New amp is deeper and taller so I needed a solution to provide deeper shelves and more clearance for ventilation. Didn't see a lot of offerings that were aesthetically appealing enough to motivate me to immediately bust open my wallet, and a few months earlier I built a "live edge" bar height table to accommodate extra seating in my listening room. The table project was fun and turned out very decent and provided the form and function I was looking for. With all this in mind I thought it would make sense to maintain a consistent look and build a rack using the same materials. Form factor of the Solid Steel rack is 3 shelves in 2 columns accommodating 6 components. I was keen on lowering the profile of the new rack as it is situated in front of an 8' casement window with a low sill so I built it using two shelves which are 65" wide to accommodate the width of 3 standard components. 
Materials used for the table and new rack are 2" square steel tubing that I had fabricated by a local welding shop. The shelves are made from 2" thick live edge pine that is milled/finished to ~1 3/4" thickness. I had concerns using pine, but after working with it I prior, it felt heavy and solid and I thought it would have the density to not negatively effect the sound in the room. The rack is located on the front wall between the speakers so I thought that by lowering the profile, there was an outside chance I might even get better sound. Lastly, when I assembled the rack, I isolated the shelves from the frame with 1" wide by 1/4" thick neoprene tape. I also used rubber washers between the screws and the frame so  the shelves and the steel frame are isolated from one another.
Once I got the rack assembled I was more than pleased with the look. I was seriously chomping at the bit to get it situated in the room with components installed but didn't right away because I really enjoyed just looking at the finished product. I recruited my son to help me move it and was really encouraged as the thing is a beast and weighs a lot. 
I installed components into the new rack, powered everything on and gave it about 30 minutes before I queued up the first song. I think I was still interested in how great it all looked when the music started but it didn't take more than several seconds to realize something had changed and I don't mean just a little. It was like someone put a blanket over each of my speakers. It seems that aside from building a fine looking rack, somehow I also succeeded in building a broadband attenuator that does an awesome job of damping most of the audio spectrum in my room and is particularly harsh on low and mid frequencies. Of course as this happened I shut everything down and rechecked and re-seated all my connections which changed nothing.
I've been super busy since completing this project but in the coming weeks will start to systematically deconstruct the setup to better understand the culprit(s). I am reasonably sure the pine shelving is at least part of it but am interested to see if the isolation technique I used is also damping the sound somehow? I phoned one of the rack companies that advertises a lot here on A'gon and a gentleman (forgot his name) was kind enough to answer some questions for me and mentioned that the coupling technique I used could be a major offender and that there are different schools of thought for when to isolate and when to couple directly. While I am going through this exercise I'll also experiment with moving my components (or most of them) from the front wall to an alternative place in the room. 
In the end I just wanted to share the experience with others that might be considering a similar effort and to say that there is much more to this than meets the eye. I didn't realize how much material, construction technique and perhaps even form factor (size and shape) can all make a dramatic difference. Since all of this transpired I've read a bunch of reviews on racks and many of them comment on the sound of the rack....I probably would have called BS on this before doing this project but now I am a true believer.