there is a reason they are short, long cables affect the sound of phono circuits, thye high frequencies are most affected. But you can experiment and maybe you won't find the difference a problem. From an electronics retailer, in USA Radioshack, obtain a pair of RCA couplers and a short cable with RCAs on each end, plug them onto your existing cable. The ground wire can be extended with hookup wire from the same place, use somethimng like black pvc insulated stranded tinned copper wire and then solder a length to the existing ground wire. Cut off the existing terminal and just strip the far end half an inch and twist it onto the ground terminal of your amp.