In many cases, tube amplifiers can be driven into clipping without damaging speakers like their solid-state counterparts often do. Plus, the Maggie tweeter is fused, so I wouldn't worry about it -- especially since you are using good judgement in keeping the volume low.
If you want to be extra careful you can always contact the amp's manufacturer and run it by them. They ought to know exactly how their amp behaves when overdriven...
If you want to be extra careful you can always contact the amp's manufacturer and run it by them. They ought to know exactly how their amp behaves when overdriven...