Can I connect a subwoofer to this socket?

[swee'pea99]

The guy in the shop said the mini speakers I bought to placate 'er indores could do with a bit of help from a subwoofer - and I'm sure he's right. Thing is, it's a standard type amp, with only standard L&R speaker connectors. He said I could connect a subwoofer to any of the line out sockets (tho' I'd have to make any volume adjustments on the subwoofer itself). Assuming that's right, is the line out you can see here (on the bottom) the right one to use?

(It's an old Harmon Kardon system, with all the components brought together and feeding into the one 'Main in' pair you can see next to it.)

Thanks for any advice.

 

[2PedalsTez]

I'm sure someone clever will give you the answer, but I'm not sure that will work.
For the sub to work from a fixed level feed it would need to be 'active' (have its own amp to drive its speaker) and also contain a crossover that ensures it only outputs low frequency.

I'm trying to figure out the pic. It looks like a pre/power amp combo, whether that would help what you want to achieve, I can't say.

 

[swee'pea99]

Sorry, I should've said - I'm assuming it'll have to be an active one.