Sv-n.t I 1-2 (introductory verse 9)

Re: Sādhuvilāsinī, introductory verse 9.

I haven't been able to properly understand the following verse:

Vaṇṇanaṃ ārabhissāmi, sādhippāyamahāpayaṃ;
Atthaṃ tamupanissāya, aññañcāpi yathārahaṃ. 9.

There's no proplem with pada 9a (I will now begin the commentary) but it is
problematic to understand the grammar and meaning of the rest of the verse
(padas 9bcd).

I first took  'sādhippāyamahāpayaṃ' to be: sa (=saha) + adhippāya + mahā +
payaṃ. The main difficulty here is with 'paya' which has the meaning of
"milk" or "water" and the great water or great milk doesn't make much sense.
Some other possibilities I'm considering are:

'-mahāpayaṃ' = mahā + āpayaṃ -- a great river (see MW under āpayā f.) -- ?"a
great river of particular meanings".

'sādhippāyamahāpayaṃ' = sādhippāyam ahāpayaṃ. CPD has 'ahapaya' in the sense
of not neglecting, not omitting. ??with the particular meanings, without
omitting,"

Could '-mahāpayaṃ/ perhaps be the name of a text?

Another problem is deciding on whether sāḍhippāyamahāpayaṃ' is an attribute
of vaṇṇanaṃ or atthaṃ.

My translation of padas 9cd is: "relying on that meaning and the other (one)
too as is appropriate" although it's not clear what "that meaning" and "the
other" is referring to. Perhaps 'taṃ' and 'aññaṃ' are referring to somthing
else.

Best wishes,

Jim