Which is the most important part of a stereo system?

It is the SPEAKERS it's an oversimplification this is where the sound comes from. Paul at PS Audio states the same thing.  If you upgrade your speakers you will hear an improvement that should be significant.

If you take a $300 streamer and $3000 streamer most people cannot hear a difference even with a revealing system but with poor speakers, you will not discern the difference.

I think it's like the old SLR cameras the body of the camera just controls the shutter so the money you put into the body of the camera didn't make that much difference a Nikon or pin hole. But it was the Lens that actually captured the image great lens great image. 

Great speakers great sound. It's like what Kevin at Upscale Audio says $40,000 turntable with a $400 cart is a $400 turntable that might be the exception to the rule

Terry9, and anyone else who thinks cables are least important:

you couldn’t be more wrong, however, it is true that much of what is being sold as hi-end cables can often hurt the sound. Believe me I know, but when cables are designed by people who actually understand the inherent obstacles to producing quality cables the music benefits. If/when there are diminishing returns it is at the very top of a cable line (when they typically cost as much as a car)

My preference is WireWorld, who offers several series to fit your budget. Also, about a year ago, they introduced Series 8. I have seen a good amount of used Series 7 as some people feel compelled to upgrade


hth

OP
2 that I am familiar with (either their integrates or as separates include; Parasound (A23 + P5) and Elac (I own the Audio Alchemy DDP-1 + PS 5 : Parasound include dac/phono, but Elac includes Streaming and their amp can be turned into mono with a flip of a switch, should you want more power with their matching amp. The Elac is true balanced!


Underwood HiFi sells the Elac among it’s many products, all with very good discounts
hth

I recently setup a pair of $26.00 3 way 12 inch woofer  speakers into another room than my usual.

6 feet apart and sitting in the sweet spot.

The sound was gloriuosly surprising.

Airy..holographic...coming from forward behind and the sides...speakers disapeared...etc...

Room.  The room is usually the hardest to change.  The room will dictate speaker and listener placement.
Once that is determined, a savvy buyer will consider speakers (including subwoofers) that will perform optimally in the chosen room.  Sound dispersion, wall, floor and ceiling reflections and absorption treatments, bass traps, subwoofer system and room loading, digital room correction will all be considered.
Once the speaker selection is pared down to those that will complement the room, the buyer will select speakers that sound "good" to him/her (or maybe look good).  Once that is settled, a good audio dealer will be able to hook you up with appropriate amplification for the chosen speakers.  Source should be considered last, as it is the easiest to change.
Note:  it is amazing how even inexpensive speakers can sound fantastic when pulled away from the walls and reflective surfaces and into the middle of the room.  I have a couple of Harbeth P3 speakers that are easy to move (I can't leave them in the middle of the room, so I put them back when I am done listening).  In that nearfield position, with me on a chair away from the back wall, It is very hard to imagine anything that could sound much better (well, actually I can, but tube amplified horn-loaded compression drivers with a custom crossover or Wilson Chronosonics driven by D'Agostino M-400s is fairly out of my budget - and wouldn't fit in my room anyhow)!