Missing from this discussion is what is the PS for? If you don't need an odd rail voltage the adjustable voltage feature seems like extra complexity with little benefit. Prudent design for audio circuits is to use topologies that are not overly sensitive to PS quality.
For TMI the old 78xx/79xx series of fixed VR (I remember when they were new) use internal process technology similar to op amps of their time, like the slow, noisy, limited gain bandwidth ua741 op amps. For those of you who never heard of a 741 op amp, you are lucky. One consequence of old technology inside the common 3 terminal regulators exhibit rising output impedance with increasing frequency. It is good practice to use capacitors in parallel to supplant rail impedance at higher frequency. I did a deep dive into this back in the 80s and discovered that using a 1,000uF electrolytic capacitor in parallel with 3 terminal outputs neatly flattened out the source impedance for a couple octaves above audio.
Newer adjustable regulators are designed with newer IC processes so just like newer op amps are higher performance than old 741, these newer regulators behave better too. Of course fixed 3 terminal regulators using these newer processes would also deliver better specs but the market is not demanding that and happy to purchase the old technology, lower cost parts.
There's more but thats enough to get you started.
JR