I agree; the stock cable do suck. Trying to push 40 watts thru 22-gauge wire is like trying to suck a golf ball thru a 100-foot garden hose.
Here's a fix that I did. Several others here have done this as well. Hopefully, you have a soldering iron and know how to use it.
1. You need 16-gauge speaker wire. Here in the states, I paid $10 USD for a 50-foot roll. Get a roll of this wire.
2. Go to Radio shack and buy about 12 (you'll mess up a few...I did) 3.5mm
mono mini jacks. The kind w/the threaded collar is best. IF RS doesn't have these, check an electronics supply house. Buy some heatshrink tubing to fit the wire as well.
3. Cut the lengths of wire to suit your needs. My front speakers have 6 feet each (about 3 feet too long, but hey, in the future I want a GIANT computer desk) My rear speakers each have 15 feet of wire.l
4. Strip about 1/4 of wire from each lead. Solder the silver wire to the center connector on the plug (positive). Solder the gold wire to the bigger, outer connector (ground). Cut about a 3/4 inch piece of heatshrink & slide it down the wire from the other end, over the two solder points. With a cigarette lighter, shrink the tubing around it. Screw down the collar.
5. Repeat step 4, three more times. Hook up your new wires and be amazed at the difference, not only in sound quality, but in how cool the amp now runs. There's a noticeable difference in how hot it gets. Mostly that it won't get hot anymore, just warm. The amp has to work a lot easier to push the current thru 16 gauge wire than 22 gauge wire.
Some things to look out for.
1. When soldering the two wires to the two connectors, MAKE SURE that the positive doesnt' touch the negative. I stripped too much wire off the positve lead of one of the wires and it was grounding against the collar (neg wire).
2. Make sure you use the silver wire as positive on all the wires. This ensures a "universal standard" and all speakers will be in-phase w/each other.
That's it. Good luck.