Never use an agent with an autonomous verb. It is very untypical of native Irish, while it is a shibboleth of non-native Irish. It has only become current in native literature very recently.
Better: "fuaimeanna a gcloiseann an t-éisteoir mar an gcéanna iad". It is perfectly possible to use indirect relative clause if direct relative clause would result in ambiguity. Compare:
an fear a mharaigh an saighdiúir: this could mean both "the man who killed the soldier" and "the man whom the soldier killed". If the latter is meant, we don't say *an fear a maraíodh ag an saighdiúir, because it is perfectly allowed to say "an fear ar mharaigh an saighdiúir é" (indirect relative clause, object pronoun written out). It is not very common, but it can be found in native literature. Panu Petteri Höglund 10:56, 25 Meán Fómhair 2007 (UTC)