Multiplatform toolchain for outputting "nice" PDF

For some historical reasons (and maybe others, I don't know), the tool =
chain used in the project where I'm in charge of the manual uses a very =
outdated tool chain based on the following elements:

=E2=80=A2 DocBook XSL Stylesheets 1.75.2 ("dbk") or above
=E2=80=A2 DocBook XML 4.5 ("docbook-xml-4.5")
=E2=80=A2 fop 1.1 ("fop-1.1")
=E2=80=A2 libxml2 2-2.7.7 ("libxml2-2.7.7")
=E2=80=A2 Saxon 6-5-5 ("saxon")
=E2=80=A2 XMLmind Web Help Compiler ("whc")
=E2=80=A2 Ant 1.7.1 or above ("apache-ant")

I'm still investigating the reasons why we're stuck 15 years in the =
past, but I'd like to move on.

Currently, the PDF that's built from our DocBook set is, not visually =
pleasant, to say the least.

There are few contributors to the documentation but ideally I'd like =
something that works equally well on the three major platforms that are =
Linux / Windows and macOS.

A friend of mine who also is a DITA specialist converted the set to DITA =
and semi-automatically produced a really nice PDF and there are no =
reasons why we would not be able to have something equally nice with a =
modern DocBook toolchain.

So the question is, what are the options?

Thank you in advance for your help.


--=20
Jean-Christophe Helary @brandelune
https://traductaire-libre.org
https://mac4translators.blogspot.com
https://sr.ht/~brandelune/omegat-as-a-book/