I had a tube DAC but comments here helped me understand that tubes in the input chain might be removing too much information. So, now, they're out.
Adjustments come, in descending order of impact, from
(a) tube preamp input tube and
Some adjustments also come from
(c)alternating between SS and tube amps and
(d) adjusting room treatments.
I have not found cables to move the needles significantly for my setup. The other variables have a much larger impact.