I had some people come in to hook up my rear speakers and run the cables on top of the ceiling.

All looks good, everything is tucked away neatly (after opening up the ceiling in 2 places, plastering it and painting it again) but my sound volume is gone.

They used 10m stereo cinch cables and I guess that that results in a lot of loss. I am on a low budget so I've been using (for years) a 5.1 creative labs set that has decent volume output and the source comes from my Creative Labs Dolby Prologic II decoder (great box as it has 7 audio inputs and can do a lot).

The setup itself is fine (I'm quite knowledgeable in this), only the rear speakers are at about 10% the volume of the front speakers, even when not using surround. To make sure, I simply switched the rear cables with the front cables and even then only about 10% of volume was left.

What (and where) can I buy something to amplify the rear speakers. Mind you, they should already be amplified somehow as it is not a mere line-out.

10m shouldnt make this happen. Something is wrong somewhere most likely. Check the cables, outputs and inputs.

amplifying the signal can work, but will also increase noise obviously. if something is wrong, its better to fix this first.

Yes you'd have to be hitting 1000's of metres before you lost 90% of the sound.

Try swapping in one of the front speakers for the rear just to check it isn't the rear speakers themselves.

Most likely a short in your connectors, just one strand of wire will do that. Get a cheap ohm meter and see what you measure. Should be about 0 end to end, and infinity between the wires.

Try swapping the polarity on one of the speakers or from the amp. They will cancel each other out significantly if one is sucking and the other's blowing.

Thanks for your recommendations. I'll try that tomorrow when I get my toolbox back. It puzzled me how almost all the sound can be gone. They used a 10m cinch (phono?) extension cable. I was wondering if there was enough copper in the wires or if somehow grounds became the leads and vice versa but it did not make any sense to me. The ohm meter should give me some insight :-).