Speaker Cable Suggestion

Kimber 4TC would be something to consider. Watch for a used pair on Audiogon. You want the teflon coated wire. It's much better then the 4PR. DH labs T14 is also good. It has silver plated copper, so highs are going to brighten up. You may or may not want this. Bannana connectors are easy to swap and compare different wires.

You should also play with interconnects. Stick with known brands like Kimber, Analysis plus, Cardas, Nordost etc... You can re-sell and get your cash back. DIY cables might be cheap, but re-sale will be poor. Do searches for budget cables or interconnects in the forums. Use words like "value", "budget", "cheap" and "bang for the buck".

Be more specific in your question. What sound improvements are you looking for? What is your budget?

Good to see you going the interconnect route. I have found my CD -> Pre cable to be vital to the sound in my system. I have a Kimber Power cord on my tube pre and it cleaned up the background. As your system improves you will notice changes more because the sytem as a whole has more resolution. This is why the subject is so debated. A bad system may have no effect at all. A reference system may have dramatic effects.

One thing that would be free to try is if you have improved the speaker cables go back to your $40 monster interconnects. You may notice more of a difference with the better speaker cables in place. The power cord is a good idea as well. I have been wanting to try the Signal Cable PC too, so it will be interesting to see what you say. A power cord can work wonders on cheap gear with poor power supplies. On expensive gear it may do nothing because it has super power supplies and regulation built-in. Don't be afraid to experiment.