This is to clarify something that was being discussed on coptichymns.net but i cant comment on it over there because their registration is disabled.
In terms of the joyous allelouia for psalm 150 it does have its sources and it is an authentic hymns however not the way ibrahim ayad recorded it. Muallem Tawfik says that he learned this hymn from the Great Muallem Mikhail. He records the hymn for the feast of Resurrection. Muallem Tawfik also taught it to Muallem Fahim. The hymn itself consists of 4 allelouias and a response like IHC PXC Aftonf ... etc. Fr mettias nasr and muallem zaher also record this hymn. Fr. Mettias for Pentecost with its response as well(tarkeeb) and Muallem Zaher for all Joyous Feasts with the response as well. Also Albair Gamal from the HCOC has a lesson for this hymn on copticheritage.org and he says the response for the feast of resurrection. What ibrahim ayad did was he took the Allelouias and left the response so that they didnt have to rakib all the other responses for every feast. Personally i dont agree with it. Thats the clarification of it. WHen i learn it i am going to the learn the responses for each feast.