i don't think it is possible at all without gjallahorn, no other rocket can take down crotas shield fast enough, maybe a hezen vengence as it has 3 in the mag and doesn't cause crota to move, the deathsinger part is easily solo able, i've done it plenty of times with just a black hammer and 2 hunger of crota shots, (was testing out necrochasm, btw shit for the whole raid, apart from light pillars part). what i would do is clear left side wizard and shrieker first then right, and clear the knights with swords in the right room, and deathsingers song should start, stand at the back of the room and pull out the black hammer, it's about 6 black hammer head shots to kill her.