Purchasing a s/hand Esoteric Audio Research 802 pre-amplifier started me on the valve path. Inserted into my system which at the time was a Marantz 72SE CDP with variable output, into a Quad 405 and then Dynaudio Finale kitset speakers.
The 802 tightened the bass, improved imaging and detail, put more presence around elements of the music, and overall sounded closer to the real thing.
The biggest revelation was the impact of the pre-amp vs connecting the power amp directly to the CDP.
I ended up selling the 802 many years later for more than I paid for it.
RIP Tim de Paravicini - what a genius.