Best Stereo Upgrade Value

" weakest link " is a great general answer.

In my case, I would say adding PS Audio power regenerator was the single biggest improvement. Before it I was using inexpensive Furman power conditioner.

Next, going from Redgum integrated to Burson separates linked by Wywires Diamond cables.

And third - putting old Purist Audio Dominus power cord on the power amp.

Phono stage, speakers, turntable, in that order.

Weakest link is the place to start.

But if I had to choose, the source is the more important foundation than speakers. A $10K source with a $5K amp will sqeeze every drop of performance out of a $2K speaker and make it sound like a $5K speaker, rather than the other way around, as long as that $2K speaker is not randomly chosen.

Example I have heard:

Furutech passive power conditioner - Melco S100 with LPS - Lumin P1 - CODA CSiB - KEF LS50 Meta - Audioquest Diamond, Yukon, Coffee, Monsoon and Rocket 88 cabling.

Don't love KEF speakers but this setup taught me at least those particular KEFs can sound superb given a clean, powerful signal.

It's all about synergy.  Matching your speakers to your room and your music preferences.  Matching your amp to your speakers.  Finding the source that emphasizes  the qualities you find valuable.  The current buzz word seems to be musicality over micro detail.  Where on the spectrum do you see yourself and how much time and effort are you willing to spend to get there or is it just the dollars.  Both ways work but it's also possible to invest a lot and not achieve your goal if you aren't specific what you are looking for.

For me it's taken years maybe even decades to learn what I want to hear, what's important musically and how to get there.  My approach certainly isn't the only way but it sounds good to me and I feel I'm on the right track.

In my case, it was the pre-amp - Townshend Allegri Reference - the most expensive element of my humble system.