Before shelling out huge sums on cable, there is another option, which is to try well-recommended cables, used in some high end systems, but which are relatively cheap to buy, and of very high quality. If they don't meet your needs, then look at the expensive or exotic.
For speaker cable, I use Belden 5000UP. This is 12AWG twisted pair cable, using plenty of copper (the lower the AWG number, the thicker the wire). You can buy 7m of this wire for £14 unterminated, from a UK source, and put the plugs on yourself. If I'm wrong, and this is poor cable, you've lost £14 plus postage and packing.
If you want an overview of the science behind cabling, a good read of the "Blue Jeans Cable" website is worthwhile. You can decide for yourself if it makes sense, and it may help inform any subsequent buying decisions. When looking for interconnects recently, I paid far more attention the electrical characteristics of the wire. I would assume that where they are the same, you can buy the cheaper cable as it will perform the same as the more expensive one. I also stayed away from those that didn't release technical specs.