Verse 2.9.8

अथ यत्प्रथमास्तमिते तन्निधनं तदस्य पितरोऽन्वायत्तास्तस्मात्तान्निदधति निधनभाजिनो ह्येतस्य साम्न एवं खल्वमुमादित्यं सप्तविधं सामोपास्ते ॥ २.९.८ ॥
॥ इति नवमः खण्डः ॥

atha yatprathamāstamite tannidhanaṃ tadasya pitaro'nvāyattāstasmāttānnidadhati nidhanabhājino hyetasya sāmna evaṃ khalvamumādityaṃ saptavidhaṃ sāmopāste || 2.9.8 ||
|| iti navamaḥ khaṇḍaḥ ||

8. Next, the nidhana is the form of the sun as it sets. The ancestors love this form of the sun, and this is why, as the sun sets, offerings are made to them [or, are placed on straws in honour of them at the time the śrāddha rites are performed]. For this reason, the ancestors participate in the nidhana in honour of the Sāma. This is how the sun is offered the sevenfold Sāma worship.

Word-for-word explanation:

Atha, next; yat, that; prathamāstamite [he., prathama + astamite], just as the sun sets; tat nidhanam, that is the nidhana; pitaraḥ, the ancestors; tat asya, that [form] of [the sun]; anvāyattāḥ, are attached to; tasmāt, therefore; tān, them; nidadhati, one places on straws [or, one places offerings to the ancestors on straws while performing special rites in their honour]; hi, for this reason; etasya sāmnaḥ nidhanabhājinaḥ, they participate in the nidhana in honour of the Sāma; khalu amum ādityam saptavidham sāma upāste, this is how the sun is offered the sevenfold Sāma worship. Iti navamaḥ khaṇḍaḥ, here ends the ninth section.

Commentary:

Because the ancestors love the form of the sun as it sets, people honour them at that time of the day by placing offerings to them on straw. And while doing so, they sing the nidhana hymn of the Sāma.

If a person performs the sevenfold Sāma worship with the feeling that he is worshipping the sun this way, he becomes one with the sun.