This Behringer DI might be worth a punt, if you want something short term, or just to try as proof of concept. Less than £40.
It allows for connection between amp and speaker.
I've used one for the purpose of running a 'tap' off a PA system, with good results.
https://www.gear4music.com/PA-DJ-and-Lighting/Behringer-DI100-Ultra-DI-Box/2BI?origin=product-ads&gad_source=1&gclid=CjwKCAiAxaCvBhBaEiwAvsLmWIqwyGg1Mbmiesh5RYXHvjjP3erUCD01QnvWoh3I44iZaihW8kCNERoC8ucQAvD_BwE