Parse System Messages?

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Hey all,
Wondering if there's a way to parse system messages.

Background:
Addons like "Loot Log" post to chat via the system messages.
All chat notification addons I've tested so far, where you can define specific words to trigger an audible sound, do not work with "Loot Log" (etc) due to it being a "system message".


It's past midnight here, so perhaps I just need to look at this with a fresh brain, but nothing, so far, is jumping out at me

Any help much appreciated,
Thanks