It would help to know what you have?
Assuming they are already both somewhat equal and upscale in quality/performance, you'll hear more inprovement with an upgrade to the i/c's. And it'll be because they are "upstream" from the speaker cables.
Think of it this way, if you put the best speaker cables available in your system, if the i/c's relatively suck, and "takeaway" (more) from the music signal, you ain't gonna hear an improvement through your speakers, no matter how good of a speaker cable you use. The I/c would be the weakest link and you know what is said about a chain.
Good luck!
Assuming they are already both somewhat equal and upscale in quality/performance, you'll hear more inprovement with an upgrade to the i/c's. And it'll be because they are "upstream" from the speaker cables.
Think of it this way, if you put the best speaker cables available in your system, if the i/c's relatively suck, and "takeaway" (more) from the music signal, you ain't gonna hear an improvement through your speakers, no matter how good of a speaker cable you use. The I/c would be the weakest link and you know what is said about a chain.
Good luck!