Yamunacharya was a medieval Sri Vaishnava scholar who lived a generation or two before the time of Ramanujacharya. He is considered one of Ramanujacharya's gurus, even though they never met.
Yamunacharya wrote a work called the Agama Pramanya, or "Proof of the validity of the Pancharatra Agamas," which as the name suggests, attempts to show that the Vaishnava Pancharatra Agamas are authoritative.
In that work, he says:
Therefore, even if there were a conflict between the Bhagavan's doctrine [Pancharatra Agamas] and the Veda, there still would be option between them; but we have already expounded that there is no conflict between them at all.
Opponent's objection: However, how can the venerable author of the Bhashya [Shabara's bhashya on Jaimini's mimamsa sutras] state that those parts which are in conflict are invalid: "If there be conflict, it is carefully eliminated."
Yamunacharya's refutation: This statement means that those of frail minds, who are not strong enough to plunge into the deep ocean of rules of interpretation, must not be disrespectful to the Veda.
The opponent is referring to this sutra of Jaimini:
When there is a conflict (between Veda and Smriti) the Smriti should be disregarded; because it is only when there is no such conflict that there is an assumption (of a Vedic text in support of Smriti)
This is the reason why many Hindu scholars say that Shruti takes precedence over Smriti. However, Yamunacharya thinks that Jaimini just wrote that sutra so people who are not intelligent enough to reconcile apparent contradictions between smriti and shruti should just accept the vedic text so as to not disrespect the veda.
Does Yamunacharya think that all smritis have as much authority as shruti, or does he think that only the pancharatra agamas, which are smriti, are equivalent to the Vedas?