Chris, the splice that the contractor(obviously not a victim of audio mythologies) made was entirely "kosher"(assuming that he did the splice carefully)and there's no need to be concerned about "cheap" lampcord. It's the overall resistance from end-to-end of the wire that counts, and adding a short section of 16 or 18 gauge wire might have the effect of making a 12 gauge wire have about 12.01 gauge resistance. This isn't analogous to a four lane highway suddenly turning into an eight foot wide dirt road; relax.
