The missing piece


What is a piece of equipment you added to your system and it made such a huge impact you knew you would never get rid of it? cables, components, speakers e.t.c. for me it was a pair of Intuitive Design Gamma Summit speakers.
jughead
For me definitely my Deja Vu Audio El-34 PP tube amp, especially after getting it recapped with NOS Aerovox caps. Another piece I love and can't see ever parting with is my Yamamoto YDA-1 Dac just a superbly musical piece.
Couple years ago I had to give up my listening room which was nicely proportioned for my system. I was forced into a small nearly square room approximately 12x12. Even though I was able to move all my room treatments in, the room was a problem. The biggest problem in the square room was the loss of 3D imaging.  At the time I was using a pair of Thiel 1.6s which in the old room through a very creditable 3D image with depth both behind and in front of the speakers. All gone. The solution was to set the system up in a diagonal configuration. The results were simply amazing. I now have the deepest soundstage I've ever experienced. Instruments as well as vocals are located firmly on a stage in front of me, the speakers are absolutely disappear in the music.  I've tried a few different speakers in this configuration and all but one speaker took advantage of the layout demonstrating exceptional imaging. Not sure how long this room is going to be the system's home. But I'm not looking forward to trying to recreate this sound in a standard room. 
The piece of equipment I recently added to my system is the Silent Line Power Conditioner by Redcore audio. It bested my Synergistic Research Tesla Powercell and my Running Springs Audio Dimitri with the HZ power cord by such a large margin I sold them both and laughed all the way to the bank. The only problem is no one else can ever own a Silent Line Power Conditioner because only 32 were manufactured and built by the Arizona Audio Video Club and no others will ever be made. Such a shame as the parts to build only cost $650 and it blows away all the big boys. We are fortunate to have a club member who is a certified genius and has invented and designed much audio for many manufacturers but doesn't take any credit. I wish you all could try it in your systems. The only thing close to the Silent Line is the Isotek conditioners.
Well, I wouldn't quite characterize it as 'The Missing Piece'; however, I would describe the Studer A820 reel-to-reel deck as adding a wonderful dimension to the listening experience.