Some enlarger manufacturers, primarily European ones like Kaiser, Durst,
etc.) calibrate their heads in density units while US companies
frequently used CC values.

Use the setting in your manual for your enlarger as a starting point.
Print a normal neg with a full range of tones or, better yet, a step
wedge, and see how close the print is with normal processing time. then
adjust the setting on your head up or down till you have a properly
exposed and proper contrast print.

Here's my take:

Most VC papers yield something closer to grade 2.5 without any filtration.

So a starting value of say 40Y + 35M is approximately 05Y.  The reason the
paper and enlarger makers give values with both yellow (lower contrast) and
magenta (higher contrast) values?  Balanced filters are supposed to give
equal enlarging times, for medium gray or some other arbitrary tonal value,
as you change contrast.

I have found that just adding yellow or magenta to white light works for me,
exposure times are shorter.  How much to add?  Keep in mind I use an older
Durst, but 15 yellow or magenta is around a grade, 30 is two grades and 60
is about 2.5 grades.  I usually just add PC or Ilford cut filters to my
filter drawer or use PC3 under lens filter kit.

Omega D-5 CC filter lists are all over the web try Googleing.

[Specifics snipped]

Either, or neither. Presumably, both your enlarger manufacturer and Ilford
have run tests to find what filtration settings produce particular
contrast grades; however, chances are you aren't really concerned with
hitting exactly grade 2 (or whatever) contrast. Rather, you're presumably
concerned with getting a print with contrast that's suitable for the
negative you're printing, combined with your personal taste. Both the sets
of settings you see will vary the contrast you get, and you can use either
set of numbers as guidelines -- if you get a print that's too flat, use
the tables to adjust for a higher contrast grade, etc. Alternatively, you
can just "wing it" and adjust your magenta filtration higher to get a
higher-contrast print (or yellow lower, if you started with yellow
filtration). You might want to keep notes to figure out what sorts of
settings produce good results with your negatives, and you might even want
to adjust your film development if you find you regularly need extreme
filtration to get good prints.

No filtration might or might not produce a grade 2 print; it depends on
the paper, the light source, and other factors. Certainly there's nothing
wrong with starting with no filtration and then adding magenta or yellow
filtration to increase or decrease contrast, if that first attempt was
off.

Many manufacturers provide two tables of filter settings. One uses minimal
filtration for minimum exposure times, but this means that if you change
filtration, you'll need to adjust exposure in a way that may be hard to
predict. The other table is designed to produce constant exposure values
and vary only contrast. This can be easier to use to adjust contrast, once
you figure out what shade of gray is being kept constant. These
constant-exposure tables might not apply well across brands of paper,
though.

   Most VC papers are "normal" contast, i.e., grade-2 with
unfiltered light. The dual filter values are for equalizing
the exposure times between grades.
   Try the Polycontrast values but each make of paper is
somewhat different in required filtration. Try e-mailing
Ilford, they may have values for the Omega dichroic color
head.