Do a load test with existing 70v speaker runs before jumping on a new amp. If the load test is suspiciously high, or suspiciously low, check all the 70v speakers. Make sure nobody has hooked up a plain old 8 ohm speaker in a back room or custodians shop. That could cause most of the symptoms you're reporting.

Sometimes the thoughts in my head get so bored, they go for a stroll through my mouth. This is rarely a good thing.