The Ben Ish Hai (Rav Yosef Haim of Baghdad, 1839-1933), in Parashat Vayigash (10), writes that if a person hears a Beracha while he recites Pesukeh De’zimra, he should answer "Amen" to the Beracha. Even though generally one may not interrupt in the middle of Pesukeh De’zimra, one should interrupt to answer "Amen" to a Beracha. The Ben Ish Hai cites Rav Haim Vital (1543-1620) as reporting that this was the practice of the Arizal (Rav Yishak Luria of Safed, 1534-1572), to answer "Amen" to Berachot he heard while reciting Pesukeh De’zimra.
This applies throughout the Pesukeh De’zimra service. Whether one hears a Beracha during Ashreh, one of the "Haleluy-a" Psalms, "Vayebarech David" or "Vayosha," for example, he answers "Amen." It occasionally happens that as one recites Pesukeh De’zimra, he hears the person next to him, who arrived late for Shaharit, recite the Beracha over the Tallit or the Tefillin. Or, if one arrived late, he might be reciting Pesukeh De’zimra while the Hazan recites the Beracha of "Yoser Ha’me’orot," for example. In all these instances, one would answer "Amen" to the Beracha he hears, even though he is in the middle of Pesukeh De’zimra.
If a person hears Kaddish while reciting Pesukeh De’zimra, then he should answer the first five "Amen" responses, until and including the response of "Amen Yeheh Shemeh Rabba…Da’amiran Be’alma." He should not answer "Amen" to other parts of Kaddish ("Titkabal," "Yeheh Shelama" and "Al Yisrael"). It should be emphasized that whenever one answers "Amen Yeheh Shemeh Rabba" in Kaddish, he recites all twenty-eight words, through "Da’amiran Be’alma." Although the Shulhan Aruch rules that one should say only, "Amen Yeheh Shemeh Rabba…Yitbarach," our custom follows the practice of the Arizal, who held that one should continue the response through "Da’amiran Be’alma." This applies whenever one answers "Yeheh Shemeh Rabba," even in the middle of Pesukeh De’zimra.
Halacha requires beginning Ashreh immediately after the conclusion of Yehi Chebod. After one concludes "Ya’anenu Be’yom Kor’enu," he should immediately proceed to "Ashreh Yoshebeh Betecha," without any pause or interruption. Therefore, if a person is reciting Yehi Chebod and foresees that he will hear a Beracha or Kaddish upon concluding Yehi Chebod, he should pause in the middle of Yehi Chebod until he hears the Beracha and Kaddish, and then resume his recitation of Yehi Chebod. This way, he avoids having to answer "Amen" in between Yehi Chebod and Ashreh. If a person was compelled to answer "Amen" in between Yehi Chebod and Ashreh, then after answering "Amen" he should repeat the final three verses of Yehi Chebod and then immediately begin Ashreh, so he fulfills the requirement of juxtaposing Yehi Chebod with Ashreh.
Summary: It is forbidden to make any interruptions during Pesukeh De’zimra, but if one hears a Beracha during Pesukeh De’zimra, he should answer "Amen." If one hears Kaddish during Pesukeh De’zimra, he answers the first five "Amen" responses, until and including "Yeheh Shemeh Rabba…Be’alma." A person should try to avoid having to answer "Amen" to a Beracha or Kaddish in between the end of Yehi Chebod and the beginning of Ashreh. If one had to answer "Amen" at that point, he should repeat the final three verses of Yehi Chebod and then immediately begin Ashreh.
