Hello Matt.
I don't know a lot about SPL or impedance so rookie question ahead. I can look up what it is but what I need to know is how crucial is it to know exactly what you would need? I know different instruments have different requirements. How do you know what you need or what you should be looking for in the specs if you're not sure what you need?
I hope that made sense, sorry if it didn't.
Take care,
Anita