The other advantage using a long interconnect to amp run as opposed to long speaker cables is that you can use balanced cables for the interconnect. Though I don't think that XLR helps a lot in short lengths, it does in long ones since most interference that the wire picks up along the way (antenna effect, EM inducted currents...) should be cancelled out by the balanced cables. Speaker cables can't do that. Also for most cable questions check out www.cardas.com. They have a great tech section where they explain a lot of the physics involved in cables.
