Today I just bought a pair of subwoofers from a guy at a Swedish forum www.minhembio.com
The price was 1820SEK for a pair including shipping and insurance. He will post them tomorrow so I should have them on Wednesday or Thursday I guess.
The plan is to put them in small sealed boxes, about 30 litres net volume. Power them with a Behringer iNuke NU6000DSP and use EQ to boost the bottom. I have contacted Ingvar about the boxes and hopefully he can cut all the panels for me, it depends on how much it would cost though.
I will use Neutrik speakon contacts. Between my HK amp and the Behringer I will use RCA in one end and XLR in the other (I think that works).