The singular, most significant item any of you can buy is a USB microphone and measurement program. It terms of sound quality everything else pales in comparison. Those of us who have experience with this die laughing when people say they can do this by ear.
Best Stereo Upgrade Value
A question for you audiophiles...
What "upgrade/change" has singularly given you the biggest (not incremental) improvement to your stereo system? Upgraded amp, pre-amp, tubes, room correction unit, subs, connectors, cables, speakers, streamer, stylus, speaker placement, acoustic panels, etc.?