Does anybody have any experience of Heco Activ 200/k monitors?

I found some in the basement at work and they seem in good condition (ish). I can keep then if I want, but they seem to have a weird audio connector; kind've like a male XLR but with thinner prongs...

I'd love to try 'em out, but I can't work out the connector problem.

I know I'm a newbie, but I'd really appreciate any help...