This is the most confusing answers to a simple issue. He dances all around the facts, like he is scared to death to state the truth.
The truth....
Every audio source worthy of being called Audiophile is VASTLY better than even the best speakers in every possible way. In other words, it is true the speakers can only reproduce whatever they are fed, but what they are fed in most like to be an order of magnitude higher quality than the speaker can handle.
Just look at the typical performance characteristics of two common sources versus typical speakers playing at reference levels in an average room:
THD
Vinyl = 1.0 - 0.1% (depending on cartridge, frequency, and outer versus inner grooves)
CD < 0.001%
Speakers >1.0%
IMD
Vinyl = (audible, but far too much variance to summarize)
CD = Near or below audibility
Speakers = Audible in most cases
In-Room Frequency Response
Vinyl = 30 - 18,000 Hz +/- 3dB (effective)
CD = 5 - 20,000 Hz +/- 0.5dB
Speakers = 30 -20,000 Hz +/- 6dB
Effective Dynamic Range (assuming room noise floor of 45dB A-Weighted SPL)
Vinyl = 40 - 60dB (dependent on frequency, cartridge, and outer versus inner groove region)
CD = 96dB
Speakers < 60dB
Frequency Dependent Phase Shift
Vinyl = Measurable but minimal in the audible range
CD = Inaudible
Speakers > 480 degrees (typical two way system with cone/dome drivers)
Channel Inbalance
Vinyl < Approximately +/- 0.5dB depending on setup and outer versus inner groove region
CD = 0dB
Speakers = From 0.5dB to well over 6dB depending on speaker design, placement, room acoustics, and seating position
Added Resonance, Ringing, or Decay
Vinyl = Inaudible, if at all present
CD = None
Speakers = Massive! Speaker resonances and ringing, early reflections & room echo, and room reverb add significant resonance to the signal source
I could go on, but the point is pretty much made in these aspects of sound which obviously make music sound better or worse.
So, even an affordably average turntable setup is likely to be significantly higher fidelity than even the most high end speakers. Does improving the sources make a difference? Of course! But what makes more of an appreciable and enjoyable difference - slightly and audibly changing the clarity and dynamics by upgrading a turntable, or finding the perfect set of speakers for your tastes, room, and desired listening levels?