By far for me new amps. Upgrading from what I thought was an awesome and venerable Classe stereo amp (CA 2300)_ to Audionet Max monoblocks was eye and ear opening!
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.?