100v Line Transformer

Hi Everyone.
I have an amp that is 4x200w, and I am wanting to make it 100v for some distributed speakers on two of the channels.
The speakers all have transformers in them and are tapped at various wattages throughout each line on these two channels.

My questions come with regards to installing a transformer between the 8ohm Amp and the 100v line.
Will a transformer from an old speaker work? I have a transformer from an old speaker that had many taps/windings, one of which is 200w, the speaker it was installed in had an 8ohm driver. Would this work on one of the lines? Actual load on that line is likely to be around 150w at maximum, which it is likely to never run at. Would this work? I assume you would just adjust the volume of the amp channel to affect the whole line on that channel without causing any issues with the transformer?

If not, what type of transformer should I be putting in here? Any links to actual products would help a heap also.

Cheers,