As a band director and audio professional, I understand where you're coming from.
Wireless - meaning running off batteries - isn't going to provide you the Umph, definition and clarity you're going to expect to get.
I know what kind of SPL (sound pressure levele - volume) you're talking about keeping up with, and that doesn't come cheap.
Additionally, you're going to need something that provides as much directivity as possible to keep from feeding back into the pit mics, especially if you're wanting to use the amplification system in/near the pit to keep the mallet's sound originating from there.
Let me ponder this a bit, and I'll get back to you. I'm sure others will chime in before I get back.
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